Often times, you can think of a character and label them much like we do in RPGs and MMOs (sorry this might be the DotA in me talking)
Ness and Lucas are both short - mid range casters, meaning they heavily rely on their specials and not so much on the A button. Not to say they both don't have excellent comboing and sending abilities.
Now think of how a Ness/Lucas player plays. I don't use either myself, but I do play a decent Lucas a lot. (Not to say he's a pro)
I find they like to keep a distance, use an ability or two, normally stunning with pk fire, and then following up with a combo, throw or smash. That's their general strategy, again I'm not claiming to know Ness/Lucas.
Now Olimar on the other hand, is seen as a mid-long range sniper of sorts. He does heavy melee damage, which is hard to defend or counter as Ness/Lucas, and he can quickly change to a powerful smash send, and both of them are lightweights. Olimar also has his latch ability, by clinging a pikmin onto Ness/Lucas, they either take a decent amount of damage or knock it off, 1-3 hits depending on the color. In that time (which is a lot thanks to their laggy moves) Olimar will run + grab, throw, beat down, spike smash and whatever other fun stuff. Basically, their opposite types.
I see it as an archer killing a mage. They're fast, sneaky and powerful, while the slow yet powerful mage takes his time to hit. Now think of Olimar's main counters. The Starfox crew, Shiek, and other fast short ranged heroes, err I mean characters. Olimar is hard to fight at a range, but easy to wreck close up.