Excellent post. Also IMO Mario and Sonic come from an era were Video Games were marketed almost exclusively towards children and young teens. Having a cute marketable character helped. To be Fair to Sonic the 2-D iterations were excellent and so was the cartoon series around its lore. Mario had few missteps in that area including that one awful live action movie .
Nintendo did much better creating different games in different genres utilizing the Mario Brand, games which were also critically excellent such as Mario kart. Most importantly perhaps Mario was a able to make a spectacular transition into the 3-D realm, where as Sonic Adventure was a good game but not an all time great title. Mario Party, Mario Tennis etc. We're very good games even in the begginng. Heck Mario RPG is considered a classic proving that Nintendo was very cautious with it's franchise character. Sonic had a few spins off that were mediocre like Sonic R or terrible like the one Sonic title that was a Mario Party clone... I had it on DC and I even forgot its name lol.
Well from my point of view Mario also managed the transition to 3D because he wasn’t a one trick pony. There was a freedom that allowed Mario to do what ever was needed to make 3D feasable. All sonic had was speed and ”blast processing” whitch severley restricted what you could do with him when going 3D.