Not sure where this slander for VectorMan popped up from, but he is absolutely a well-liked character. Both in and out of retro gaming scenes. I think he has only really come up a lot because he was absolutely beyond perfect for Transformed. He literally turns into a race car and flying vehicles in his games already.
Characters like Gilius Thunderhead are absolutely popular too, but if you really wanted to pull people in you would have characters people obsess over like Kazuma Kiryu, Bayonetta, Segata Sanshiro and Ryo Hazuki. Any one of those characters would have brought in a good chunk of fans that otherwise do not have any interest in this game. And there absolutely are more beyond that.
I stand by my feelings that Sonic, Robotnik and Tails are the only characters that are distinctly needed in a game like this. Do you really think huge Sonic fans that lined up to play the last dozen or so games without most of this game's cast in it are going to boycott this game for skipping out on Cream?
Also, Project X Zone 1 and 2 did great without Sonic characters in it. Even after like 90% of the diehard Sonic community complained about that too. People are really underselling the appeal of SEGA's IPs here.
Zavok is the only real dud in the cast. As for the rest of the "nobodies", I frequent the Sega Heroes Discord and I can tell you that requests for more Sonic characters like Silver and Blaze are far greater than those for other IP (which sucks for me because apparently nobody wants the ChuChus or a Kapu Kapu).
What about the chao? and Omega?
I am a mod in that discord and have seen the requests. Silver and Blaze are high, but the most requested characters are not Sonic related. Not sure if I am allowed to discuss who is, but there are several above those two. Beyond that as far as Sonic goes there are dozens of other non-Sonic characters requested after the third most requested Sonic character.
Also keep in mind that just because someone is highly requested does not mean they will happen or that they are even viable. Like say, Miku Hatsune probably aint happenin' especially considering she is not a SEGA character.