Sonic doesn't have bad matchups [he has a bazillion even matchups though].
He just has a ton of bad players who lose as soon as you figure out how to deal with spindash.
Ike is still a bad MU, theory and results both show this, regardless of spindash being used or not. The only Sonic who has beaten an Ike at the top level is Seagull Joe vs San. Every other time the MU comes up, the Sonic either loses horribly *Rango vs 6WX* or the set is close with Ike taking it *Ryo vs 6WX*
Sonic has NO real way to approach Ike, he can't do it without spindash, and spindash only increases the problem: How does a character with no way to get through a sword approach a character with super huge hitboxes, damage and kill power. Add on the fact my best approach option involves me going into a position where I can't shield, and has a linear approach option.
Add onto the fact N-Air/F-Air, our two best options in the neutral for the MU, BOTH got buffed, so it's even easier to swat Sonic out of the air and take 20-30 percent for trying to approach us. Sonic can't force an approach either, as his only answer is to yet again try to approach into a sword hitbox. AGAIN.
On the topic of Ike buffs.
This F-Air buff...
I've never had so much fun diagonal spacing characters like Cloud in all my time playing Smash. Cloud has very little answers in an air-air battle if Ike isn't directly above him because he literally has NO diagonal options that beat F-Air. The MU got so much better for Ike with the F-Air hitbox buff, if Limit wasn't so easy to get I swear we'd win the MU.