This is pikachu's worst match-up. It was more or less confirmed by the pika community a couple days ago. Admittedly this might simply have something to do with pikachus play style, but short of a major revolution on pika's tactics for this one match-up and practically speaking this is a terrible match-up for pika. Honestly though it hurts it has little to do with yellow pikmin or olimar being better at camping or how strong his kill moves are, it's entirely to do with his ridiculous grabs. If he had a normal grab this match-up would be more or less even.
Oh yeah, olimar is pretty bad offstage though against pika. Like, I find him the easiest or second easiest character to gimp and one of only two characters that pikachu's weak tailspike actually works on (the other character being link). Also, I wouldnt recommend olimar's whistle unless you are bad at di'ing, and I've never seen anyone pass through a thunder from one side to the other for any reason, so if you encounter a thunder coming back to the edge just hang out and wait till its gone. Basically if you can be hit by a thunder you will be, if you can avoid it the best way to do so is with good di and just staying away from it.
Also QAC isnt something worth emphasizing, anyone is capable of punishing a QAC if theyre not vulnerable and its predicted.
There are a few things that prevent pika from being hard countered though. The first is that olimar is freakin' slow and pika is very fast. Pikachu's awesome spot dodge helps him to punish olimar's laggy attacks and slow (but amazing) grabs. In contrast to what I read in here, if pikachu get's inside he is indeed dangerous. A simple uptilt, fair, uair, and sometimes dtilt or grabs can lead to a long string of attacks, and olimar is incredibly easy to juggle (which I double checked with your frame data). A simple fair , utilt, nair alone can do 25%, but the strings can but longer depending on how technical the pikachu is. A good pikachu will limit the fair/spot dodge or really any use of dsmash since it is easy to di out of, it's more of a quick punishing move for things that need an extended hitbox like spot dodges, landed air dodges or fairs that hit weakly.
Also it's not a big deal but its worth noting, fair and dair go through olimars upsmash. Probably not yellow, and Im not sure what other moves or smashes that applies for.