All kinds of wrong.Dolphin Slash also has A LOT more horizontal range than shield grab too. It's like DDD's shield grab range or longer. I'm not 100% sure, but angling DS may affect the horizontal range it has (like angling forward to hit with max range). People tend to fail their DI when you use it OoS really fast or when you escape with it at the last frame, making them either die pretty early (around 100% for most characters?) or get sent offstage in a bad position.
And I think against Diddy using Fair or Nair just before landing is safe on block (it's like -4 on block when hitting a shield and landing the frame afterwards or something). You can land and shield cause Diddy can't shield grab (only monkey flip, which is slow OoS) with a Banana on his hand (banana glide toss is like frame frame 8 or 9, 6 or something when down thrown). Though space that at least a bit so that he can't Down glide toss OoS you, which beats shield I think. The only reason people say Diddy's OoS game with a banana is good is because it hits so long on frame 8 or 9, but for Marth, the difference between facing a frame 6 OoS move and a frame 8 one makes quite a difference. It's not as easy when he has a banana + a banana in front of him on the ground though, so don't let him get control of 2 bananas.
First of all, doing that means you'd PS the banana, which causes Marth to trip most of the time because f**k bananas. OR you're holding shield now, waiting for the hit confirm on your shield to punish which doesn't come so you react slower so a GT up while going forwards will still get you grabbed a lot. OR he throws it up and backwards causing you to start to get camped again and you can't jump into him while the banana is in the air since it controls that space so you're now getting camped by Diddy which is miserable.
That -3/-4 number is if you land on a very specific frame(s) of fair/nair relative to the hitbox you put out.
Bananas thrown down trip through shields so GT down OoS will still trip you through your shield.
Yes, in super duper theory land, Diddy can't hit your landing with a banana throw because you're going to PS the banana and before you trip, with your frame 1 reaction time, are going to DS OoS so you hit his outstretched arm. But, here in the land of reality, unless the Diddy Kong player is an idiot (because that magic safe fair/nair have to be done so precisely, they're stupidly easy to predict which is why you see Marth's fairs get PS'd soooo often) and LETTING themselves be put into such a specific spacing for that to happen consistently, landing with aerials where there's the possibility for Diddy to shield is NOT safe. Obviously you still want to land like that sometimes so it represents the threat, but landing like that like you would vs Falco is asking for any competent Diddy to blow you up.
The DS stuff was right though.
Also @ whoever actually asked the question about DS, don't neglect DB OoS and fair OoS.