I don't think so.
I think Mario is greater than or equal to Squirtle.
Squirtle gets gimped easier, because Mario can cape stall. Mario can gimp easier, because he can cape recoveries.
Squirtle may be a bit faster, but Mario has many pluses.
Mario can camp, he has a projectile (which he can use to help with approaches and/or force approaches)
This puts him at an advantage that Squirtle doesn't have versus characters like Donkey and stuff that are slow and lack projectiles.
He can combo just as well as Squirtle, so that is not much of a big split.
Squirtle has a bit better ground game, hardly anything though, because Mario's is superb too. Squirtle and Mario both lack KO power, but Mario has better smashes. Squirtle does have the deadly D-throw though, so for KO I'd say even or very slightly in Mario's favor.
I think they are virtually the same, the only thing that makes Mario out-shine is his reflector and projectile. The spike helps, but not significantly. Squirtle's B-air and F-air basically = Mario's B-air.
Prove me wrong.
Magik:
Why is Squirtle bad? I sometimes feel he is the best out of the three, although I have started noticing Charizard's potential.
I feel Ivysaur is the worse, Squirtle has good combos on some fat characters, lol.