Not a specific problem other than I can't seem to find a weak point in Pit's game, nor can I figure out an advantage that Sonic has over him.
Kinzer basically reinforced what I already do, which actually is helpful. If I know I'm at least on the right track, then it's just a matter of tinkering and refining, a "keep doing what you're doing" kind of thing.
But yeah, the power shield thing doesn't work. Tried it. Link's arrows, yes. Pit's arrows, no.
That makes the problem a bit harder indeed... Going trough air could work, if he's bad at aiming his arrows. This is just theory, but you could try approaching with ASC shield cancel on ground. Or SDSC up to him, quickly. They get scared when you run up, then you quickly SDSC.
Let's break it down:
What does Pit have that Sonic doesn't have.
Multiple jumps
A recovery that flies you around half of Hyrule
Spammy Arrows
Hyayahayayah Rings
An arm extension (his miniswords)
A shield (not very useful, but still)
It seems to me his major advantage is not being approachable.
What does Sonic have that Pit doesn't have
2 chargable roll attacks that look exactly the same
A Spring (too useful)
Shield Cancel approaches (Think of SDSC, ASC to shield, running shield)
An unforgettable speed.
Rolling attacks
Good for having Pit put up an arrow, making him wonder if it's down-B or side-B
Can be used to approach, due to Spindash's invicibility frames
Spring
Pit's recovery might be awesome, but when he uses his up-B and gets hit, it's bye-bye Pit. If you see him use this, dont go after Pit, drop a spring on the fool. Also fun for double jumping, fall above his head, SPRING, down-B (canceled or not)
Shield Cancel Approaches
Great! When you get up to him, you have more options than him. You can Shield Cancel, faking out your opponent. If you fight opponents who do not know of ASC, first use some regular continueing ASC's on him. Then use it to approaches, but cancel it, and grab the fool!
Speed
You're Sonic, you have speed. Be creative, use it to not get spammed.