Sonic can't sell as a niche fan pandering 2D fast jumping game.I'm not trying to portray Sega evil and Nintendo good, here. There's just the reality of what works both franchises. Mario is multifaceted since he's a funny looking human that's also a plumber. Tremendous amount of direction you can go with that, and thank the heavens Mario hasn't gone "full anime" like Sonic. Nintendo knows Mario's lane. Sega only recently understands what makes Sonic work is the old school scrolling action starring an cute 90's mascot.
I also don't buy your "blatant pandering" comment. Old school fans, such as myself, know what makes Sonic work. He goes fast in one direction. It's never worked in full 3-D and all those Sonic Adventure games have aged like milk. Sega had overextended the brand because it's their mascot and they were gonna do whatever they could to keep him relevant. Unfortunately, he became a joke. I've always viewed Sonic as a one trick pony, but a classic one at that. Sega ruined Sonic with so many failed modern attempts. Square peg, round hole.
Don't even get me started on the diehard fans. Sega went full anime with Sonic and that has to be the worst aspect of them all. It's attracted all the weeaboos with its inane story and characters. This is what ultimately turns so many old school gamers away from Sonic. There's nothing edgy about what Sega has done with Sonic. It's a teenage weeaboos wet dream with all that anime bullshit. We all know what you can find in Google image search if you start looking for those Sonic characters...
Sonic has always been what it was suppose to be; A basic side scrolling 90's mascot that goes fast. That's what old school fans love about him. There's a lot of beauty in that simplicity. I think the reality for many of the diehards is they don't realize they're no longer the target audience. You're too old to be giving a shit about the story or characters of this franchise. It's for kids. Let the kids have their fun without the older gamers trying to force some semblance of "maturity" into the franchise.
It's like being in your 30's while still being a Power Rangers fan and expecting the franchise to grow up with you. No, dude. You grew up. In the meantime, lets hope Sega keeps letting Sonic do what he does best. Fast, 2-D scrolling action. If Sega can stick to that, then they have my attention. It's something I can enjoy with my nieces and nephews. Kind of like every Mario game. Funny how that works.
They have to do something with him to sell. Unleashed, Colors, and Adventure 1 and 2 had issues, some would say they are bad games, all sold over 2 million copies.
Issues Is Sonic has trouble selling 1 million in recent years outside Mania because the games aren't finished and bad. But the good ones that people like did sell.
I think the solution is to swap out teams for Sonic. Sonic Team can't make a 5 million copy selling Sonic even if they cut the price and give it away. But Crash can even after a 7 year hiatus. That's pretty telling.