Doc is just Mario with a cheap B^, better dair, massively overpowered attacks, and a horrible recovery. And there's nothing Nintendo can do to change him, as he's nothing but a spin-off character.
He should leave, as should Pichu and Roy; everyone else should stay.
The Ice Climbers and Ness should not leave. They are retro characters and - especially Ness (massive EB fanbase to this day) - are quite popular. Why
should they leave, anyway? Because they're old? Samus, Mr. Game & Watch, and Pit are also retro characters. Each installment in the Smash series brings new classic characters to the fray. Why remove some of them when Nintendo keeps adding more?
EDIT:
1. On Smash 64 Mario could use Mario Tornado really good as a quadruple jump. In addition, I could link that move up with most of his combos.
His B-down is still an excellent recovery tool in Melee; but I don't really see why you'd use it as an attack.
2. His aerial linkers were unmatched, meaning I could link up his aerial combos to a certain extent.
Considering his uair, nair, and bair are still amazing comboing/juggling attacks, I'd say your point here is also valid in Melee. However, I do agree that his fair and dair are rather crappy (ugh, his dair is the most useless move in the game, I swear).
3. Even though that you couldn't charge his Smash moves, they were way more powerful than they are on Melee.
But, of course, everyone was stronger in SSB64 than they are on Melee. You could KO people off the sides and top of the level at like 80% damage with pretty much anyone. And I actually find Mario's smashes to be rather powerful in Melee still.
4. Can you say, King of Combos? I can!
I've basically already addressed this point.
It's not that I didn't enjoy playing as Mario in Melee, all I'm saying is that he needs a major tune-up in Brawl.
I do agree with you on this. Well, not a major tune-up; more so a minor one. He's one of my favorite characters to use; but it's so frustrating considering how
hard he is to use. I'd like it if they made his fair and dair not totally useless again.