Sorry for bringing back the Tekken comparison, but I feel like I should mention this
Tekken Tag 2 is VERY balanced in spite of its large roster (which, honestly, has so many clones) because the game has so few stuff that could be considered broken or unfair (there's like, the Mishima's EWGF and some other launchers?) and the game actually isn't that complex at all, not even high execution outside backdash cancelling and other moves, it just has a lot of depth. The tag team mechanics and the way the game is designed in general gives pretty much every character necessary options to compete. I'm no dedicated Tekken player though, so I'd appreciate if someone else can expand on this, or even correct me if I'm wrong.
Smash is actually really complex and there's a lot of nuances here and there. Stages play a laaarger role than they do in Tekken, you have more movement options, DI, fall speeds, overall aerial mobility, etc etc etc. Every traditional fighting game player I know that tried Smash actually think the mechanics are way too convoluted. Taking this into account, there's bound to be characters that could abuse the system.
You're right, Tekken is NOT a complicated game, it's just a very deep one. There are alot of nuances to everything and while no system is particularly complicated, the amount of depth they create is pretty massive. It's why Tekken has nothing like 1-frame links, and its buffer is extremely lenient, but 2D fighting players will say the game is too hard to learn.
As for balance, here's why I say Tekken Tag 2 is a good example to follow, even for Smash.
Tekken is a game built around options. Instead of most 2D fighters, where specific characters fill a specific niche, Tekken is a game where EVERYONE is given a basic set of options and they work forward from there. Everyone can low parry, MOST everyone has a mid parry option of some sorts, everyone has the same general options on the floor, everyone has some version of a hopkick / standard launch punish, everyone has multiple grabs types, ect ect ect. And then from there, the moveset lists are pretty big, and the game's mechanics are vast, so they can add a unique identity from multiple angles than just shoehorning a character into one. You've got the Mishimas and their punish game, tricky characters like ling/Lei, versatile characters like Law, grapplers, ect ect.
And this is why Smash 64 is most balanced smash game. It's not its roster size, it's how they designed characters. Smash gives every character a standard set of options (roll, sidestep, airdodge, ect) but it doesn't expand that past defense and evasion, and so when it comes to offense, some characters are inherently given options that others don't have. But in SSB64? EVERYONE has a kill throw. (nearly) EVERYONE has a sex kick Nair (that kills/gimps). Z-cancelling wasn't based on the previous animation -- it removed ALL landing lag, for everybody, it didn't matter. I believe every character in SSB64 had a 0-death combo except for Samus. I think.
Melee was close...but it's where the big differences started to arise. But again, everyone could wavedash (and thus edgehog), everyone had a reflector (due to powershield), everyone could L-cancel. Melee gave every character alot of options.
Brawl chose a different path, where combos became more limited and the game was a bit more methodical instead of technical. And this
actually would have worked pretty well, but there was one or two characters who just had vastly better options and it skewed the meta. (not to mention tripping)
And here in Smash 4 we've come to yet another issue with non-standard tools for dealing with offense. Shields have been buffed, which inherently buffs punish options, which inherently nerfs offense. And thus, the current meta is skewed in a direction that favors characters who can poke fast or get high reward off a grab. Your Sheiks, Diddys, ZSSs, Falcons, and Marios.
This is why i think the nerfs to shieldlag/shieldpush and buffs to evasion are so painful to this game's meta. Characters like Zelda
desperately need those values in order to justify their unsafe and risky movesets, but it's just another pressure option completely removed. Something as simple as removing the ability to push a defender off the ledge is a massive nerf to hard hitters and slower characters.
IMO if Smash would just revert its shield properties to brawl levels, a bunch of mid/low tiers would instantly shoot up the list.