I've been playing and Oli main lately, most Olimar practice I've gotten in a while, and, while Olimar can rack up damage hella quick from a distance, I have the feeling that he can do very very little against Wario's pressure game once he gets inside your range.
Dairs shred pikmin (and you), nairs take them off him instantly, and Wario is a pretty good gimper. Haha, I recently found that Wario's sh actually sends him perfectly over the Pikmin sent out in a Pivot Grab (similar to how he can sh perfectly over ZSS' stun gun)... this isn't matchup breaking but it's nice to know, especially since you're a "sitting duck" until the pikmin gets back. What else, if he pressure chases you offstage and gets within range, he can actually nair for a guaranteed hit, as, if you whistle cancel, you'll block the first hit of the nair, but not the second. The waft is also actually VERY VIABLE in this matchup at ANY TIME. At lower percents it will send you almost perfectly horizontal, so if you get hit by it, it's an easy gimp setup. Also, if Pikmin are latched onto him, WATCH OUT, as the fart hitbox duration will be extended as it kills the latched Pikmin. I haven't paid attention to the colors, but Wario's upairs will oftentimes both destroy your Pikmin during a dair AND hit you.
On the flipside, you guys get some heavily damaging early combos on Wario, can make it difficult for him to get inside your comfort zone, your nair and uptilt **** him (be careful though, they have little range, and thus are easily/safely baitable, and they can be SDId), and your purple upsmash > Wario (as well as any yellow aerial pretty much. You want to stay grounded, but at the same time you can't rely entirely on your grabs, as, since you're Olimars, that's what we're expecting, and you won't get even a fraction of the grabs you're accustomed to. PICK A HUGE *** PLATFORM STAGE THAT YOU CAN STAND UNDER (not really YI, the plat slants and gives Wario more room to maneuver), and you can make life hell for Wario. Just, if you see him getting past your grab/aerial defenses, RUN, if you stay stationary you will get bitten, and that's horrible as it will set you up for a massive ****** pretty much, lol.
I know it looks from the way I posted that Wario has many more things going for him, but this isn't the case, Oli's damage racking is absolutely ridiculous, and he can actually kill Wario at a decent percentage. I do believe Wario has advantage over Oli, but I wouldn't put it higher than 60:40. I will update my opinion as I play more/different Olis (should I ever, lol).
P.S. Wario can pop a wheelie and you can no longer grab him off the bike when he does so. You can risk it and go for an upsmash, but it's safer to just shield and let him ride past you.