I respect the opinion but I believe he is a low tier character. Not really what I'd call bottom however, but this is, after all, just me. I don't think he's super garbage or bad, nor do I think it is an exaggeration to say that about 75% of his kit is better Mario moves (probably more like 85%).
His niche is being remarkably functional in what he actually does relative to public perception however.
This, This so much. Doctor Mario is such a cohesive & straight-forward character: A Brawler with everything good about Brawlers ( Explosive & consistent advantage state in nearly all areas through a set of moves that can possibly lead into others, along with some options to punish the basic answers your opponent would be tempted to pick, a fair amount of non commital moves that go along a bait & punish playstyle that Doc pulls off quite efficiently despite his lack of mobility, most notably thanks to his low SH re-enforcing the ability to throw out moves & move along, perhaps the most complete out of shield game in the entire game, the best anti zoning tool in the game in SH Cape that also serves as momentum reversal for the sake of mixing up both your movement & landings, along with the fact that some of Doc's moves can already allow him to beat certain projectiles ) but also nearly everything bad about Brawlers ( Mid Range game is rather bad & the rare times you'll ever be winning these kind of battles is because your opponent allowed you to get a little too close, you got some kind of read or approached in a way they did not expect OR Doc's frame data beating the opponent's moves. Either way, most characters, especially those with the disjoints, will be giving Doctor Mario a tough time in this precise area. Long Range game is also not exactly stellar, or rather, it's pretty bad: Pills can't force approaches all that well, and the rest of Doc's moveset simply isn't long range/zoning based. As i've mentionned before though, the saving grace of Cape and its consistency mitigate this issue and along the outrewarding in advantage state that goes in Doc vs Zoners matchup, these usually belong in the better matchups for Doc )
I would also like to come back on the whole disadvantage state talk, which is my main point of disagreement, althrough i can totally understand those who would be tempted to believe that Doc has a below average disadvantage. As you already know, Doc possesses 2 Frame 3 moves in his arsenal, being Nair & UpB, along with a nice weight/float combo that allow him to not be prone to combos & has among the better overextension punishes out there, although depending on the character, it could be more or less efficient. I would have been tempted to call Doc's landing bad, and i still wouldn't say it's good, moreso against mobile characters, but it has been getting better and is filled with enough options to give most of the character a decently hard time punishing Doc's landing: the momentum reversal with wavebounce cape, along with the good frame data which plays an important role in the offensive/punishes options Doc may have out of an airdodge, and the aggressive landing options makes for a varied enough threat. Finally, Doc's recovery. I'll be honest, i won't argue that it's good, or even that's it's not one of the worse in the game, rather, i would just like to remind that Smash 4 isn't Melee or Brawl: the potency of an airdodge into UpB, as dumb as it may sound, is good enough for most situations. I'm not saying you won't get edgeguarded, i'm saying that, like most characters, you shouldn't get edgeguarded too often. If you do, it's still usually your fault. Doc is also decent enough at avoiding constant ledgeguarding, through the potency of his SH AD options ( either Nair or UpB after are usually the most commonly seen ) , said potency also adds an option that should definitly not be slept on when it comes to approaching.
So what have we learned? I would love to say nothing, because honestly, what i've been going through is rather basic stuff: a reminder of the options this character has in order to achieve victory over the opponent, and with that in mind, i wouldn't say it's very hard to get a simple idea of what his matchups look like: Disjoints are his hardest matchups, while a majority of the Brawlers & Zoners? Doc fares decent enough against, minus a few exception for specific reasons, because the neutral becomes evenly-matched and while Doc has to fight characters with perhaps more options through their mobility or some of their moves' consistency, the fact that Doc nearly outrewards most characters on trades, that his advantage state is consistent enough to only need a couple of strikes & a bit of neutral play before becoming threatening to the opponent's stock, grants him some good to decent matchups against characters above him, like Mario, Lucario, Fox or Villager. On the other hand, struggles can be seen against characters near him or even below, with characters like Palutena or Dedede being capable to fight back or even beat Doc through some of their good options.
Tl;Dr Doc is a pretty straight-forward slow but powerful brawler with everything you can expect from a brawler, whether it's good or bad. His spot on a tier list is dependant on how much you value counterpick characters, and how highly you think of a character who's most likely needy of a secondary to get past disjoints ( & Sonic ) OR could potentially do some damage given the right bracket ( Despite me mentionned disjoints being annoying for Doc, it's an advice, not a necessity: Most of his matchups against these characters are perfectly doable, and we've seen upsets of Docs against characters who possesses disjoints, such as Mewtwo with B7Games' 2-0 over Abadango, or 2ManyCooks' win over Mr.E )
Either way, given the development of all the characters surrounding Doc and the fact that we do need characters in the Low Tier: Yes, Doc's probably around the low tier as of right now, because with his pathetic representation ( I believe there are more recorded sets of MII GUNNER than of Dr.Mario, i might be wrong though, but that speaks volumes about Doc's representation in tournament ) hasn't allowed him to show all the potential improvements & gained consistency that make him a valuable character. However, he remains an interesting pick for certain characters: the heavy grapplers for example, could benefit from a character with a much better Fox matchup with a neutral that doesn't feel too alien to them ( i.e: A few options used in different ways, precise movement along with it as a means of baiting the opponent into a wanted move, the presence of a kill confirm, and for Bowser/Charizard, the presence of an excellent out of shield game )