imo fox destroys mario.
just remember to reflect fireballs and not get stuck in one spot. fox can use platforms to his advantage by moving in and out faster than mario ever could, and fox's lasers are really good at pinning mario down. a lot of people get hit by fireballs when trying to spam lasers when they should be taking advantage of the platforms.
yeah, fox is easy to edgeguard, but that's true against any character, and fox is really good at edgeguarding mario and covering all the little tricks that he can do to try to get back on stage. if he's trying to recover from above with fireballs, you just have to time a bair before his fireball animation is over. you can bair through his fireballs and knock him out. if mario is recovering from below, you just need to be patient and dtilt when necessary. if mario uses down b, you have all the time in the world to see where he's going to end up. sometimes you can just bair or shine after down b, sometimes you can edgehog and regular ledge get up into whatever (depending on mario %).
if mario is already grabbing edge, fox bair covers ledgejump ----> everything except for mario up b i guess, but even that is pretty risky for mario. i personally think it's easier to get back on stage once you're grabbing the ledge as fox than as mario, or at the very least it's equally difficult.
even if fox is easier to edgeguard, i feel mario has to take more risks in the neutral to get anything started. upsmash is pretty risky if you miss and can get you pwnd, everyone can di out of dair, uair only works at mid---> high %. if you think about it, mario is kinda like a ****ty fox with a slightly better recovery