They do point out that the "skill" is not really "skill", just rote memorization and trial-and-error.
Also having straightforward speed with exploration is rather contradictory. They point this out as well. It's a game that encourages going forward but also encourages you to take your time and go through each level in a nonlinear fashion.
Skill is absolutely skill in this game. Memorization is only necessary for parts of the game that are
actually bad, poorly designed, or poorly executed (case and point- labyrinth zone)
It's not
just memorization and trial and error. You need good reaction time and and a good understanding of how sonic moves and how to manipulate him to make him go and do what you want. The game is all about momentum based platforming- sure theres some trial and error- but mario is guilty of this just as well.
Their whole point about the game encouraging moving slowly- more often than not that is simply not the case. Almost every level in sonic 2 encourages going fast, and only punishes you if you don't stay on your toes while doing so. You need to pay actual attention to what's going on- the game runs at a steady 60 fps- and you have a few different moves to combat/dodge oncoming enemies, it's not hard to press down to roll into something or just jump over it.
Complaining about the loop de loops, rolling hills, corkscrews, and other parts of the game where all you do is hold right is such a stupid thing to argue as a flaw. That's like complaining about parts of mario where you aren't jumping and stomping goomba or breaking blocks.
The level design is all about speed- even if there's multiple paths- usually it works like this. The higher the path- the harder, but also faster. The game is about risk vs reward most of the time with it's level design- not that there aren't exceptions to this- but thats typically the case.
The other thing they fail to mention throughout all of this- is that while you sure will take more hits in this game than you would in mario- You almost never die due to it. In mario- it's 1 or 2 hits and you die. Sonic can take as much damage as you want him to- as long as you have at least 1 ring- which aren't exactly difficult to obtain.
tl:dr-- The Classic Sonic games are well designed games and- while they do have their flaws, saying they are overrated isn't exactly accurate, and their argument for it is rather weak.
Saying Sonic overall as a franchise is overrated on the other hand is completely accurate. There are so many bad sonic games it's not even funny.