Why even collect the Emeralds if they don't do anything except for the Sonics? Why even hunt for tokens? Why even explore? If you're not playing as Sonic you might as well just rush through every level, fight the final boss and the most you'll be missing is a cute cutscene. It shouldn't take long until you realize that you're looking at the wrong incentives and forgetting about the ones that started this discussion to being with.
Super forms are optional: you don't need to use them. They're temporary. They are supposed to make up for at least some of the players' weaknesses as a reward
I'm confused. I have never been trying to make a case against super forms, nor against them being optional, nor against them being a buff.
I would actually go so far as to say that in the game's current state, Super is only optional at all if you are Sonic or Metal. In any other case base form is mandatory, the option isn't even there. Super Forms are the incentive for going after the emeralds at all. If you aren't Sonic or Metal, or playing with someone who is, there's no point.
I'm entirely in favor therefore of everyone having access to Supers as a reward for collecting the emeralds. If you don't want to, you don't have to, but if you do then it's there. My intention from the start was merely an attempt to find a way to allow for this that is in line with the official reasoning for why they currently don't have the option.
Nothing that I have suggested operates as any sort of debuff to the characters. Things such as Amy having a stronger, further reaching hammer and Knuckles having Multi-Glide are flat buffs to a characters moveset, and even being able to lose a certain amount of rings getting hit as a Super Form is something that has occurred before in the games. This does not contradict the logic of what a Super Form is.
It seems as though everyone replying to me is under the impression that a Super Form is only a Super Form if it has total and complete invincibility to everything, but that simply isn't always the case even in the official games. I will admit I have never seen a Super Form that doesn't experience ring drain, but that doesn't mean it couldn't exist for a character such as Amy. As far as I know Amy has never even had a canonical Super Form, so anything could be possible really.
The argument that super forms remove character variety is itself a fallacy that leads to ad hominem Rebuttals. In S3K itself, Ignoring the flikies, Super Tails gets a flying speed boost that complements his play style. Super Knuckles gets a gliding Acceleration boost and a speed boost in climbing walls witch complements the way he plays.
Sonic only gets Invincibility and a speed Boost because his gameplay is just that basic form. SRB2 and Sonic World Both are the only games I know of that allow you to hover as Super Sonic in a level.
My own suggestions for Tails and Knuckles involved them gaining speed while using their respective abilities. I'm not sure what exactly you are arguing against by making this point.
S3K is a great game, and the Supers within it reflect it's design quite well. Collecting the Emeralds is largely the primary incentive for exploring the levels at all. By the time you have access to your Super, getting to the end of the level is more your primary objective, so the forms being based on speed makes sense within this context.
In SRB2, collecting the emeralds is only one incentive for exploration. There is also the emblems, which unlock things such as bonus levels and ways to find more emblems. Characters such as Tails and Knuckles therefore now have more reason than ever before to slow down and explore, and to continue doing so even after they have all the emeralds. Some players will just want to get to the end of the level as fast as possible, and my suggestions do help with that. Even with Amy, who wouldn't get a speed boost at all, would have an easier time dealing with enemies while transformed and could launch herself much further with springs.
More importantly however, the forms would also act as an assistance with the playstyle they already have, based around exploration. By designing the forms in this way, you accommodate both for speedrunners and for those who wish to use the forms without needing to rush to the finish, as opposed to just making them like Super Sonic in which case there's a heavy bias in favor of speedrunners. Designing them like that doesn't do a lot to help those who just want to use them to more easily explore the levels and collect emblems, and also limits the pathways you can efficiently take to the ones with easiest time keeping up your ring count.
I also disagree with the entire notion that these wouldn't be true Super Forms. They would do the same thing for every character as they do for Sonic: Boost the potential of what they are already best at.