I planned on getting a laptop that could run Melee on dolphin at 60 FPS. If I could also run Brawl I suppose I could try out Brawl netplay.
Personally, I don't really think a ratio of Mario players dictates where a particular Mario may or may not place. However, I do think that the ratios of every other character will help you determine where he'll place. If you have a high percentage of bad matchups in a tournament you can rest assured that you won't place top 10% without some crazy luck or unless they're all seriously bad. However, if you're in some kind of scene that's dominated by Olimars or another one of Mario's solid top/high tier matchups then as long as you're skilled enough, it's within the realm of possibility.
However, the tournament scene at the mid to high level is dominated by Meta Knight, Mario's worst matchup in my opinion. Mario literally can't function competitively on his own, a Mario player will have to be just as skilled with a much better character in order to stand a reasonable chance of winning anything. And at that point it's much simpler to just main the other character, unfortunately.
This brings me to a pretty similar point. It's hard to improve by playing the best players unless you're placing where the best players are. If you consistently want to play against the best players, you'll have to get to the top 10% of placings. That's why it's extremely difficult to improve at a high level with Mario. At a low level it's easy to improve, you probably wouldn't be placing much better with a better character anyway. At the mid level it's significantly harder than a low level, but you can still improve at a reasonable rate. At a high level? You're statistically not going to make it that far into tournaments, so the only hope is to have a practice partner who is a high to top level player. But that's not always reasonable and I'm not even convinced that would help a particular Mario place far enough to be relevant in bracket.
TL;DR Mario can't do very well even in a tournament even if piloted by a great player. He only really works as a dual-main or secondary in a competitive setting.