The thing is, the Links between games are incarnations of the same hero; the same person, in a way. Scourge is very much a different character than Sonic just as Groose is to Mido.
Not really. Scourge before was just a more jerky Sonic with a black jacket, shades and some boots. He didn't become his own identity until the Master Emerald gave him a paint job and blue contacts.
Besides, the two have a struggle towards each other in regards tot heir personalities because of how different they are, but how easily they could turn out just like the other, which gets brought up at times by Sonic by him remembering Scourge taunting him with saying he knew the real reason he can't stand him.
Scourge is like Dark Pit/Pittoo from Kid Icarus: Uprising. He's very much his own character due to the amount of depth given to him and having his own personality, but he's still very much an alternate version of the original he's based off of. An "alternative possibility" as to what they could be like, if you will. But even then Dark Pit is still Pit and Scourge is still Sonic. Dark Pit is another side of Pit's mind and heart while Scourge is literally Sonic from another universe.
So I'd say he still counts.
Actually, the only major difference is that Classic Sonic's torso is about twice as big, and his legs shrink appropriately.
These two models are sharing the same bones. It needs some tweaking so that Classic Sonic's arms don't clip through his belly especially in some of the more extreme poses, but it all lines up rather well with the hurtboxes.
That's not a different model. They're sharing the same bones because that's a vertex hack. one that usually comes with resided animations, too. XD
I've actually used it and it doesn't line up with his hurtboxes that well at all, honestly. He often ends up looking like he's floating around instead and his polygons either stretch out farther than his hurtboxes or not far enough. It's not the best example, honestly. That's why I didn't suggest that version of Classic and don't really support Classic at all but at least gave an alternative version of him that could work in the post you quoted.
Honestly, if it's gonna be an alt for Modern Sonic, let it be an alt that already works with Modern Sonic's design. Hence the ideas I stated and why some want Darkspine Sonic.