To preface anything I have to say here, I don't really have any stakes in this discussion because I don't even like to use super forms as they currently are in normal SRB2 gameplay, I feel that being invincible takes away a lot of what I find interesting about the game. But I've been thinking about this and had a few ideas about super forms in SRB2 at least, and how to make them more interesting and unique for the other characters.
I agree that super forms made the characters in S3&K play basically the same, but I definitely don't think that would be the case in SRB2 because it's a game where each character is very ability focused and going super would not take away those abilities. I also think that writing this off as a "vocal minority" is very disingenuous when this discussion comes up with each major release and there are a few different people involved each time in addition to the regulars arguing for more super forms.
I do think the other characters shouldn't get the same type of super that Sonic and Metal get, however, so here are a few alternative ideas I've been thinking of that hopefully keeps what makes these characters interesting intact.
Tails: With all 7 emeralds, Tails could get back their super jump from the pre-2.2 era of multiplayer supers. Where pressing spin while in the air would launch them high into the air, and instead of a normal super transformation they could just use this super jump at will to give them extreme vertical mobility at a cost of 10 rings per jump. Enhancing what makes Tails unique (vertical movement is what they specialize in any way). This could also be linked to a super transformation instead, which wouldn't make the player invincible, increase their normal movement speed and would not drain their rings. But require the player have 50 rings before unlocking the super jump that drains 10 rings per-use.
Knuckles: I think Knuckles could get a conventional super transformation, but without the invincibility or movement speed increase that the others are associated with. Instead of letting him destroy enemies around him by gliding into walls like with his hyper form in S3&K. Enforcing the idea that he's a slower but more deliberate and powerful character that seems to be encouraged in 2.2. To balance out how he won't have invincibility in this form, the ring drain could be at half speed or maybe it would just cost him 10 rings to use the wall smash when gliding.
Amy: I like Amy in this game specifically because she's the underpowered challenge character. I think that's a genuinely interesting part of her design that adds more to her than people seem to be giving it credit for. But if she had a super transformation, I'd be happy to see it focus more on her hammer and how she attacks instead to focus on what makes her character unique. Giving her hammers attack significantly longer range, making her spin in the air with the hammer for a longer time after activating the ability so the timing is less punishing, or maybe even giving her a
hammer jump in a super transformation (which is something I see people request relatively frequently!). And if a hammer jump is used, make that cost 10 rings peruse after transforming instead of the regular ring drain to discourage that 'gotta go fast' mentality that is the reason the other characters can't turn super.
Fang: It seems wrong for Fang to have a super form to me, especially when he already has a
rad flying bike in Triple Trouble called the Marvelous Queen. Just frame getting all 7 chaos emeralds as he uses them to repair the bike, or maybe he just uses them to buy the bike. And at the cost of 50 rings Fang can activate it and ride that instead of a normal super transformation. Which could give fang a two-hit shield and enhance his spring jump by using a spring on the bottom of the vehicle instead, either by giving him a higher tail bounce jump or enhancing his mobility in the air while bouncing. Alternatively (or maybe in addition to this) it could also give Fang the ability to fire his popgun while moving. Given the player would be paying the 50 rings cost of super upfront, there would be no need for a ring drain effect here either.
Anyway, those are my ideas on super forms. None of the characters mentioned above would have normal super forms that drain rings to avoid the current problem where it encourages all of the characters to go fast all the time. And in fact, having conditional abilities that drain rings on use would encourage the player to take it slow and explore a little more to collect rings to allow them to use these abilities more often. Hopefully, this contributes something to the discussion then!