But what is wrong with Meta Knight, Pit, and Olimar? They were just fine from the original Brawl version. I don't think its necessary to alter them what's so ever.
Meta Knight is one of the least changed Brawl characters ironically. He's still speedy, can combo well, and can gimp easily. Because of Project M's speedier physics and more movement options, many characters are able to overcome Meta Knight's speed and mobility, which was dominating in Brawl. So aside from tweaking his recovery and certain overwhelming traits, he didn't need to be changed a lot, so he wasn't.
The only thing really wrong with Brawl Pit when transferring him to a Melee environment is his recovery. Sure, the original Wings of Icarus was easy to interrupt, but ultimately it's just easier to make a new recovery method for him then try to fix Up-B to a point where it's not...stupid. Also, Angel Ring.
I can't really say much on Olimar yet because he just came out and I don't try him out a lot, but I do wish he had a least one more Pikmin. 5 is just a nice solid number.