Truuue.
But let's take a look at the current Top-Tier characters...
Metaknight - Insane priority, great speed, insane recovery, insanely fast moves
DeDeDe - Insanely strong, has chaingrabs, has projectile, sweet b-air
Mr Game and Watch - insane priority, absorbs energy based projectiles, insane recovery, fast smashes
Hmmm it might be easier to show you a link... wait 1 minute please.
Ok here you go:
http://www.smashboards.com/showthread.php?t=199108
This basically explains why characters are in the Top Tier...
Sonic is fast in the air and ground... but he has low priority on most his moves, and his smashes are very fast at all. His recovery is good though. So at best, I think he could make Middle Tier...