Hello! I finally decided to make an account after looking at this site for a long time.
Ever since Unleashed in 2008, it seems as though Sonic Team have been reluctant to include other playable characters in games probably due to the backlash against sonic games having too many characters. I think this is where I think people haven't really been clear in explaining what the real problem is. I don't think it's the friends themselves that are the problem though, it's the forced unnecessary alternate playstyles that detract from the core Sonic experience that is. Sadly most of the alternate playstyles in Sonic games feature his friends meaning these two were bound to be associated.
Unleashed proved that you don't need other playable characters (unless you count Gaia colossus as a character) in order to introduce a forced alternate playstyle and Mania (and pretty much every other 2D Sonic game) proved that you can have many playable characters and still have a solid focused game.
There was this random thread on Reset Era that basically inspired me to make this one. It talks about how Sonic is actually ahead of Mario when it comes to playable female characters in a platformer game! I wanna play as Blaze, Amy, Cream & Cheese, Rouge (and maybe even that new character Tangle) in a mainline game again and I wanna see them done some justice!