Like... I dunno. I've never understood the ire against any comeback mechanic. Like, there is this impression that if something can even remotely be misconstrued as a comeback mechanic, its awful/evil. The only case I ever really agreed with this is X-Factor, but when I look at several other games, I really don't find any comeback mechanics I find fault with, including SFV.
There are certainly varying degrees of egregiousness when it comes to the implementation of comeback mechanics. First I'll go through some other series before coming to Street Fighter.
The most recent example is Tekken 7's Rage system. Now Rage DRIVES are something that I kinda like tbh. While it is also a comeback mechanic, you have to work for it. You can never just throw a rage drive out there and expect it to work (OK, an argument can kinda be made for Gigas), it's a part of your toolset that meshes naturally. The passive damage increase while you have rage and most importantly, the rage arts are REALLY fucking annoying. They can all be blocked/ducked and then punished in full by pretty much every character so it's not too bad but it adds an almost Street Fighter-ish element to the series that I just don't like because it feels like it's giving too many options to the defender. If he's down on health that's cause he got outplayed and the loser should have to hold that. The damage scaling with how little health you have is also REALLY annoying.
In the case of KI, some are definitely better than others. The S1 cast has arguably the best instincts while S2 and S3 instincts are almost all just bullshit. You can do stuff like invincible reversal cancel into instinct and then react accordingly if they blocked it or got hit (though this can be avoided by moving backwards so that the invincible reversal whiffs entirely) so I don't really mind the activation of it. It's the buffs that the character gets which REALLY annoy me. Eyedol can do literally safe dps where the only way to punish is to use a projectile invincible shadow move. Tusk can cancel his DPs into stomps and other stuff so fuck punishes. Basically they just remove all modicum of skill and awareness by just letting you do whatever and then making it safe and even creating mix up opportunities. S1 cast mostly has to actually work to get something off of those instincts. They buff the abilities that they were already good at, but they don't affect the weaknesses. Orchid can make her DP relatively safe but she has to spend a firecat to do that and time it properly. Jago can get health back but he actually needs to hit a fireball to do that, etc etc. So the S1 cast is decent in this regard but the S2 and S3 cast is extremely fucking annoying.
KoF's comeback factor of giving you meter when a new character comes in is something I really have liked. You still have to work if you want that comeback but having meter gives you the tools to work towards it. It makes comebacks easier but in no way "guaranteed".
MvC3's is the absolute worst. Just shit. Literally nothing creative or good about it. Fuck that.
SFIV's was actually kinda medium in the sense that while it was one opportunity to deliver an intense chunk of damage and straight up win the round sometimes, that was the only chance you had. If the opponent had a read then you're eating a full punish most of the time. It wasn't great but it wasn't the worst.
SFV's idea of the V-Trigger is... not a bad one inherently. Like many things, it's the shitty fucking balance that just ruins it. If V-Triggers were used as tools to react to jumpins, react to fireballs rather than the "hit sweep and cancel into V-Trigger into setplay" which we have now then that'd be infinitely preferable. Some V-Triggers are still decent like Birdie's. It gives him the tools to comeback but those tools still aren't strong enough to the point where he's broken or that his weaknesses are nullified. Some V-Triggers make an already annoying character moreso like Laura and Necalli.
But the common thing among all of these comeback mechanics is that I don't like them (with the exception of KoF) and they don't just give the loser a fighting chance, they give them the means to completely turn the tide. When the amount of work you have to put in for a comeback is LESS than the amount of work your opponent put in to have you in this situation, you know something stinks.