I never understood complaints that Kanto in GSC was bad. It's not supposed to be a second main quest, it's post game content, of course it's gonna be more streamlined.
I liked that its way more open and that it assumes the player already knows this terrain, and has already become a champion, so they throw it like a large playground for them to do whatever they want. I love it, and Pokemon has sorely missed this kind of mindset for the past years.
It's only bad if you want it to be a main quest, which it's not. As post-game content, which it is, it's incredible and way bigger and meatier than anything we have ever seen since (except for HGSS, which threw a Battle Frontier on top of it).
If it happened today it would be celebrated as a huge feature, buuut since it's from gen 2, it's totally okay to shit over it.