Mario got a personality (canonically, at least) the moment Charles Martinet started voicing him. He joyously shouts as he successfully performs feats of agility on his strangely merry way to rescue a princess whose cake he thoroughly enjoys; all in spite of the constant dangers he faces in the form of pitfalls, sentient mushrooms, and giant, fire-breathing turtle... Bull... Thing... Bowser. I'm talking about Bowser. He speaks broken English, dreams of Italian cuisine, and cried when an obnoxious talking water spigot "died." He frickin' cried! If you think LUIGI has a personality and Mario doesn't, you haven't been paying attention; Luigi - within the context of the main series - is pretty damned similar to Mario. He boasts a more or less down-pitched version of Mario's voice; coupled with the same enjoyment of his own peril-dodging, gravity-defying antics on his path to do the same things and accomplish the same goals (and with similar Italian stereotypes intact). Mario got a personality first, and Luigi followed suit. Mario, as fleshed out by Martinet, was essentially the basis for Luigi. And that's still true even from a character design standpoint; the two used to be identical twins. Mario / Jumpman / Mr. Video came first.
If you like Mario, you should like Luigi; and vice versa. We're not talking Sonic vs. Tails, here.
You played Super Mario Bros. 2 (JPN) / a.k.a. Lost Levels? Luigi jumped higher, yes, but he also controlled like a skater on an ice rink. By comparison, Mario stops on a dime. You're speaking entirely in RELATIVE terms, here. Luigi jumps comparatively higher than Mario, and Mario controls comparably better than Luigi. And yes, Peach can float. But - in Super Mario Bros. 2 / Super Mario USA - her lifting speed is different (and I believe slower) than Mario's (Toad's actually the weight lifter in the group, apparently), and, in Super Mario 3D World, I'm pretty sure her movement speed is slower (again, Toad's a quick little so-and-so, by comparison).
If you perceive Mario as being average, it's because he was kind of what they based everyone else around. Luigi jumps high because he was made to jump higher than Mario. Peach's floaty ability stands out because Mario didn't have it (and, if you wanna be technical, she inherited it from the Doki Doki Panic character). Hell, I've read that Smash-ability for individual characters was originally based around Mario's character in the Smash Bros. series. Mario's the character you pick when you want neither an edge nor a handicap, but that's the character's strength from a game play perspective.