Well, yeah, that's the theory. In practice first place is the easiest place to be in for a multitude of other, non-blue-shell-related reasons and the blue shell is an attempted bandaid fix that punishes skill and doesn't equalize anything.
No, not a theory. A proven fact. That becomes clearer the more you study MK's design.
Obviously, the Blue Shell is a catchup mechanic. Being a racing game, players are meant to gun for the first place, stay in it and finish in it. Thing is that first place is actually one of the least interesting places to be in, and driving in it uncontested for the rest of the race way ahead of the pack is not fun at all. It is also not fun to be in dead last and having no way to prevent the players in the lead from getting farther away. That makes the race become less interesting for everyone involved if this happened; hence why the the blue shell was designed. The shell creates problems of its own, which is why players in the lead can never be allowed to spawn them and it's only obtainable by those in the back can get it. The blast radius is designed so that the explosion takes the player in second if he/she is neck to neck with the first place; forcing them to slow down or swerve around it, which in turn may allow players behind to catch up. A close game makes the race much more interesting.
Of course, getting hit seconds before the finish line can ruin you which sucks for people who are committed to mastery of the game and want their superior skills to be acknowledged. The blue shell doesn't always allow a player with the better skills to win, but this is not much a big problem as people make it out to be even at a tournament level if the player has some way to counter the randomness. A bad draw in a Poker game may handicap you but it doesn't guarantee your loss. For these most skilled players, the designers made the blue shell avoidable in certain circumstances that casuals tend to overlook. You can play around it by doing the smart thing and preserve certain items like the Star, Boo, Mushroom, or the Horn; if you lack items to assist you, can brake so that second and/or third place go down with you, or you can intentionally let someone pass you at the right time so that the Shell targets them instead. If you are a good player, you can still have some agency and mitigate the danger of the a Blue Shell somewhat. Recent iterations like MK 8 have actually improved counterplay by adding double items and tools like the Horn, which shows that the devs have given tournament play some considerations.
Granted, there are still going to be times where a late game blue shell is going to rain on your parade and make you want to curse to the heavens. Even if it doesn't feel like it at times, that item makes it for tighter and more enjoyable games. Which is why I called it "a necessary evil".
Unhealthy? Boring? You mean like the way of SSB4, which many said was more balanced than previous titles? And now we have the same being said here, but as time goes on, we'll see who's viable and who isn't. A balanced game provides variety, so you have a very strange view of what constitutes as "unhealthy" and "boring".
I said 45:55 is realistic. I never suggested or implied that it was easy, but I would have to say fewer characters or a lot more development would certainly help reach that goal. Chess and checkers lack particular Nintendo characters I'd like to play as, and while I do like a game of checkers, it's not a game I'd pursue professionally.
For all its imbalances, Smash 4 was still a fun game. True, there were elements that needed to be fined tuned like Bayonetta, but there was still enough variety in the game.
You call my views of what is boring and unhealthy 'strange', yet there is irony in your statement when on your second paragraph you say that fewer characters would help achieve that goal. You don't see that that actually kills variety?
Devs should prevent to balance a game where every class, etc. feels the same and has equal opportunities against each other. Perfectly balanced? Yeah. Is it fun? Probably not.
Going to back to having fewer characters, you could do that and indirectly buff some fighters as a result. Take Dedede for instance, his matchup spread suggests that he has trouble with characters who heavily rely on disjoints and projectiles. We could give him some buffs like increasing his air speed and such, but unfavorable matchups for him will still exist. So you could help him by removing those bad matchups from the game; by cutting Megaman, Villager, the Links, Marth, Ike, Cloud, Wolf, Pacman, Samus, etc. you indirectly benefit Dedede. That's a legit way to balance the game. But also an awful one, because now we took away a bunch of choices from the players.
You also suggest investing more development time, but the best way check the viability from the assets is to release your game and collect data from millions of players across the world. You can make a game with a bunch of characters with strengths and trade offs, and have playtesters try them but the meta truly begins to evolve when the consumers start playing your game.
I feel that you think that only tournament play should be taken into consideration, but the devs have to take into account all matchups at ALL the skill levels. Some characters that are perceived as great may have a low win rate online, but stats like those may be misleading. A character like Fox who fares amazingly at high level play may even have a lower win rate in lower levels of play than, say, K. Rool. And characters who are perceived as well balanced may be purposely avoided because they are not seen as fun to play as, which is why to have to take feedback and pick rate into consideration.
While you may claim how time will tell us who isn't viable and who isn't, the perception of balance is important as well, probably more than balance itself. As of now, nobody is perceiving a situation where we have a Melee Fox, Brawl MK or Smash 4 Bayonetta in our hands (yet), which is a positive outlook. And more importantly, this game is only 6 months old, so the meta is STILL developing so your claims are kinda pointless as of now. There are still several balance patches scheduled to come in the near future. Perceived weak characters will (hopefully) be buffed and if some strong element needs to be nerfed, they might do so. Just me, but it's better if we get more buffs than nerfs in the future.
You may not thought that it was easy, but I feel that the complexity of balance can't be understated.
Games should be celebrated for having a plethora of options to choose from even if some imbalances exist. Those imbalances may actually make the game more exciting to watch. Take the set of Nairo vs Light at Collision as an example, where they used Ganondorf and Fox respectively. The match was fun to watch and Nairo's victory was made more satisfying with the fact that he used a character that is generally perceived to have a disadvantageous matchup against Fox and is generally considered to be lower tier than him. If both characters were perfectly balanced and had equal chances of winning, people would have shifted from being "Wow, Nairo's Ganon vs Light's Fox? Such a risky pick with the stakes being high, so who knows how this will end up" to be like "Oh, it's Ganon vs Fox. Good luck to whoever wins".
As for Metroid pity parties, I'm just going to continue complaining. After all, casuals complain and end up getting what they want. "Projectiles are too good! Punish all characters whose mechanics are centered around projectiles!" "Nerf PK Fire! The game is four months old, but I still can't escape!" "Nerf Ness' d-smash! Yes, he's been gimped for years, but how dare he get that same opportunity as everyone else!" "Little Mac is too strong! Nerf his recovery!" Unless you use a popular character, a la Bayo and Cloud.
Mediocre people do nothing but complain and stunt their own growth. Self victimization is a disease. That's why I have little empathy for people who throw pity party at themselves. Don't understand why you would do something as unflattering as follow the example of whiny casuals rather than try to become a better version of yourself. And I also thought you were going to quit playing anyways, so I don't see why you care this much now.
-Balancing around Elite Smash is silly but so is the idea of basing it off tournament results for multiple reasons. Balancing around player feedback would be the most direct but unreliable for several reasons. So balancing around Elite Smash for now is the lesser of the 3 evils.
Feedback should be taken from all of those source you mentioned, as well as data from tournaments and online play, but good judgement needs to be exercised as well.
isn't considered Top Tier, it means I rarely encounter him anymore. (Wasn't a fan of fighting 
