I'm very much with Wyatt on this one. I went back to the drawing board after clinching a heart-attack-inducing last hit against Black Waltz at CoT4, and determined that there were quite a few things in this match-up that you can exploit in your favor.
Olimar's basic strategies are pretty linear: use Pikmin Throw to force your approach, and then grab or attack accordingly. For as good, frustrating and generally reliable these tactics are, they are also fairly two-dimensional and simple to exploit with proper harassment and baiting from mid-range. A mix-up of running perfect shields, glide-tossing, Monkey Kicks, and feint aerial approaches to grabs are actually quite effective in managing the mayhem of this match-up.
A lot of his attacks often blend together during the heat of the match, as Pikmin are thrown or being retracted or running back to Olimar. It's pretty imperative that you are able to distinguish between a grab, a F-smash and a Pikmin Throw; smart Olimars will only be resorting to specific moves in specific situations, anyway. This will be important because if you're relying on your vision to identify these moves, you also need to quickly respond accordingly and determine if and how you are to punish Olimar's cool-down (since the majority of his ground attacks are generally quick to begin with).
If you can contain Pikmin, minimize damage and constantly interrupt Olimar's ground control, the rest of the match-up becomes considerably less frustrating. Olimar cuts through the air with somewhat fast horizontal movement, but his aerial DI is very stiff overall; once he commits to a direction, he is generally going to stay on that trajectory. Olimar is very easy to harass with a torrent of smashed and non-smashed banana peel pulls and varied peanut arcs. If none of these successfully set you up for a spike or edge-hog of some sort, you should
at least be able to force Olimar to commit to the use of Pikmin Chain. Here, his aerial DI becomes even more horrendous, and you can pretty much leave a banana peel or two for him to slip on stage upon landing, or punish his cool-down with a ledge-hopped F-air.
Also, Olimar's options dramatically diminish if he is being juggled or trapped on a platform. Once you pop him up in the air, it is not unreasonable nor impossible to keep him up there.
Everything I have mentioned are all common strategic strands that I have observed not only in my own match-up experience, but videos by both Gness and ADHD. I wasn't able to find a recorded match between Wyatt and BlackWaltz (I just saw him do his damage against BW on live stream at APEX), but here are a couple of video examples of how to manage this match-up:
The tempo of both matches are vastly different, but the strategic applications are basically identical.
In the very least, I believe this to be an even match-up.