also, I'm against the rebound dash because I feel like sonic shouldn't have any vertical movement whatsoever, and he should just stick to being the amazing horizontal mobility character he is, I've said this before, but all the rebound dash does is give sonic more options than he really needs
I partially agree with this, however there is a nuance to the argument that I don't agree with. In regards to upwards vertical movement, the only situation I would be okay with Sonic having any would be in the event that either he's the only playable character, or he's transformed into Super Sonic. Upwards verticality is something that every single other has, and is distinctly something that doesn't really fit the gameplay trope that Sonic himself fits into, at least without making use of things like springs, or homing chains in the Adventure games and later. Upwards verticality is what the other characters are for, it's why you pick them over Sonic.
However, I'm more than fine with the idea of Sonic having downwards verticality. Such a thing could be used in conjunction with slopes to assist Sonic in gaining and maintaining speed, which suits him perfectly.
I'm not too sure why you would think the ability who's only purpose is to give you top speed on a silver platter goes well with a game series about attaining and maintaining speed.
The thok can give you top running speed, but it doesn't give you top speed in general. Even in Sonic 1 achieving top running speed only involved holding left or right for a couple seconds. The nuance that makes thok engaging is that if you manage to get moving faster than that, the thok doesn't necessarily slow you down and makes for a great momentum redirection tool. Whether for turning on a dime, performing a bounce off a monitor/spring/enemy at a particular angle, or a combination of the two, the thok is actually great for skill based movement that involves holding onto speed and/or making skillful use of it.
The issue with the rebound dash is that like the thok the nuance to the ability that makes it engaging is very skill based. The entire point of them removing the thok is to make Sonic more beginner friendly. If beginner players are struggling to make use of the thok, something that's largely the same thing but that ping pongs you around all over the place is only going to make the problem worse. I do enjoy the ability, but fun is a subjective thing and I personally have always found making skilled use of the thok to be more fun. The thok feels less in control early on, but when you know what you are doing it's much more satisfying to use.
While I would prefer for the thok to remain on Sonic, it being accessible in the vanilla game without mods is a larger priority for me for the sake of being able to use it on my actual save file. I do like the idea of putting it on an unlockable character so long as the character has more than just the thok validating their existence. Just as with the old Metal Sonic concept that has since been scrapped, the idea of just making another character "Old Sonic" with nothing else special to them is lame and takes away from any originality the character could otherwise have. A concept I've put forward in the past is the idea of implementing Espio as a playable character with the thok as his double jump ability. To make him more interesting and unique, he could be unable to spindash, but able to walk/run on walls/ceilings for brief periods of time (or for as long as he wants while Super) while holding down the spin button. This would make his playstyle sort of like a parkour ninja playstyle, speedier than knuckles and technically more mobile, but not quite as upwards vertical in regards to potential height gained in base form.