I'm not exactly the person to go to for this match-up because all the Pits that I ever play are either mediocre or don't even use him lol. But here's what I think.
Pit's arrows destroy Dedede. He can hardly ever get through them without taking damage.
no they don't lol. If anything they are harassment to force D3 to approach and a means for Pit to pressure him. It's not like he's fighting Falco, who's projectiles come out faster and in greater quantities, AND serve the purpose of approaching, forcing an approach, harassment, traps, retreating, and pressure so it's not nearly as bad. Also, D3's Waddles stop Pit from outright camping with arrows, but the arrows still trouble D3, I'll give you that.
D3 edgeguards Pit pretty hard. The enormous range and hitboxes on his fair and bair make very threatening walls for a recovering Pit, who must pull a Snake if he doesn't want to get walled. At least D3 can power through Pit's offstage edgeguarding with his Up-B (But there won't be anything that'll save him if Pit is on the stage when he does this. Speaking of which, the Pit must learn to punish D3's recovery. It isn't that hard - just harass him until he needs to use his up-b then **** him from there. The scenario I was talking about with plowing through Pit's edgeguarding only applies if Pit is chasing D3 offstage).
Like many other characters, Pit combos the **** out of D3. Pit also has considerable priority and some good disjointed attacks that really hurt D3, especially in the air. However, D3 has
more disjoints, and more priority and range to go along with that. All of D3's aerials except nair outrange and in some cases outspeed Pit's aerials save for Pit's bair.
On the ground, D3 has more range period. Ftilt, shield grab, dtilt, hell even his jab outrange a good deal of Pit's ground attacks (That ******* side-b is among those exceptions lol). Pit is faster tho. But honestly I think the ground vs ground game won't matter that much cause the only time I ever see Pit on the ground is when he lands upon which he attacks or grabs immediately or when he being crappy with his arrows.
There isn't really much Pit can do against a D3 who's just content to sit in his shield. Fire arrows, and he'll toss a Waddle or ftilt or just PS all of them. Aerial poking is risky because Pit NEEDS to retreat after every poke or he will get grabbed. It's extremely risky for a ground approach since there's the constant notion of that shield grab looming over Pit's head. The obvious solution is for Pit to run in and grab, and you can bet that the D3 will see this coming.
D3 kills Pit pretty early. Like at 105-110 on FD with Utilt. Unfortunately, Pit can only dream of killing D3 that early. With good DI D3 will be living up to like 120-130 depending on what you hit him with.
It's basically a game of wait for the other side to **** up. If D3 messes up, he's in for a huge hurting. Same applies for Pit; only difference is that D3 punishes harder, mainly because he hits harder.
Oh yeah, and the CG. Deals a lot of damage, puts Pit in the perfect position to edgeguard, can cause some Pits to spam Up-B to try and get out and if D3 catches on he can punish hard, etc.
If you ask me, this match is D3's favor. 60:40-55:45, slight advantage to D3. Nothing too significant that pushes it to D3's advantage, just small things - D3 outdoes Pit in the air, D3's sheer damage output combined with the fact that Pit dies early, sheer range on the ground, massive edgeguarding presence, the chaingrab, and somewhat-safe shieldcamping (I know I'm making it sound like D3 has a huge advantage, but really, it's nothing much. <_<). Pit is fully capable of doing some pretty disgusting things to D3 tho.