So, rather than be snide, I thought I'd try to write an actually informative post.
This post is very informative, and it really nails why I (and others, probably) find these games fun.
I think watching tells me the core problem I have with Sonic's design is the open ended levels. If it were more structured and linear, I'd probably like it. But instead, depending on route, you can miss entire obstacles. To me it's a bungled mess and ruins why I like platformers. The entire concept is broken to me. The result are speed runs without adversity. Dude doesn't even deal with an enemy in Star Light. If pressed, and good enough, and I am, you can ignore entire enemies on a Sonic stage. To me that is not good design.
Yeah, this reads like you really don't like Genesis Sonic games, as they're not what you're looking for in a platformer. I think the thing is, though, that the set of design decisions that you value in a platformer is not necessarily the only right way to do it. For example, being able to find routes that let you avoid enemies entirely and beat the game in a faster, easier, or just plain
different way is part of the appeal of a lot of these games.
The key thing is that the things you mention liking in platformers are not, fundamentally, the only good way to make a platformer.
I actually have a similar opinion on 3D action game combat. I don't like the slow, deliberate combat that games like the Souls series and Monster Hunter are centered around. The stamina management, especially, is really frustrating to me. I prefer a game like Devil May Cry, where you have much more freedom at any given moment to change what you're doing, dodge attacks, etc. The thing is, though, the reason why I like DMC and dislike Souls can be the same reason that a person likes Souls and dislikes DMC.
Basically what I'm saying is that all the things you pointed out about Genesis Sonic's design are true, but the conclusion that the game is unequivocally "kinda bad" is flawed and somewhat closed-minded. It's a shame that you're being dogpiled on, really; it can be difficult to see why people enjoy something that hits all these marks that you consider bad, and even I've had that problem for years. I hope this didn't sound patronizing or anything, I really don't mean it to.
Oh, and on a final note on these game's design: many of the bits with loops and corkscrews are pure spectacle and not very interactive. As someone who loves the games, that's entirely true, and frankly, it's also not a bad thing. They divide up the more involved parts of the levels, and they just look cool. There's nothing wrong with taking a break from more nuanced design just to look cool every now and then.