she can't edge snap in PM, and m2k thinks her grab game is worse (I think it's fine, for the record).
the real reason m2k thinks that sheik is worse is that she's relatively worse, because the other characters are much improved, which is a totally valid point. sheik isn't leaps and bounds better than the other characters like she is in melee. as such, m2k thinks she's just average ish, while i think she's narrowly better than the other characters. both are different interpretations of the same idea though.
Her back throw was sort of nerf/buff situation. Its a buff for some, but it was definitely a nerf for M2K who heavily relied on grabs like f-throw and b-throw to throw characters off the stage for the edge guard.
The fact that a lot of the cast has very good recoveries also undermines M2K's sheik, so there are quite a few things that play in.
I've been screwing around with Diddy, and he's actually not as bad as I thought. The bananas are good pressure and creates a lot of openings, but the fact that he's slow to take it out and throws it behind him is a bit inconvenient. A large problem with his bananas is that opponents can easily wavedash into them to pick them up, which can essentially turn the tides against you. This is the big difference between Diddy's bananas to say Peach's turnips or LInks bombs.
His side-b is incredibly situational on stage and he usually has better options. As far as edge guarding with that move goes, I'll need to experiment more with it to see its potential.
Diddy's recovery is also a bit lackluster in some areas. While he has great horizontal distance, he has an incredibly poor vertical recovery on stages that don't have walls (like Dracula's Castle).
I don't exactly know the advantages/disadvantages between d-throw and b-throw. Is one more powerful than the other? Do you have to DI them differently? I know that d-throw is good against fast fallers at low percents as both a tech-chase and/or gimp tool, but that's about it. I could see his dair becoming a great move in the future as a combo starter should it have a larger hitbox, but for now, it's a bit mediocre.
I'm a bit torn about what particular niche Diddy Kong is better in, offense or defense. He can apply a lot of pressure through glide tossing, AGT, and overall stage control with his bananas. I can see him being able to rack up some insane damage really quickly with them. He also has an above-average ground speed and a decently sized grab range. On the flip side, his AGT and side-b gives him expanded aerial mobility. That combined with the fact that his aerials hits opponents far, his bananas for stage limitations, and peanuts for keep away make for a pretty strong defensive game.
This is just what I've gathered after playing Diddy for some time. I'm sure there are more advanced players out there with better knowledge of the character than I do, so feel free to correct/enlighten me.