I wouldn't say no one plays him. Most people are just intimidated by his five trillion IQ plays.
People are also intimidated at his relatively fast-attacks with decent disjoint, and don't realize that PacMan needs to attack the opponent to 180% before he has a chance of an "easy" kill move (BAir or BThrow)
Before 180%, PacMan's kill options are... Key, Hydrant, and Smashes. I guess you can hit a weaker player with these, but they aren't easy to hit at high level play IMO.
Is there some gaping hole in his gameplay I’ve not come across yet that’s going to nerf my life?
Killing people. FSmash kills now, but intelligent opponents know how to avoid it. FSmash fails to kill consistently at jab-lock percents, so the only way you can get FSmash setup is Bell, and that setup isn't exactly reliable. Its not like Pacman has an EZ-mode Marth / Lucina's Nair (hit1) -> Fast Fall -> FSmash.
In my experience, "Killing" opponents is mostly about throwing them off the ledge and hoping they don't figure out my Hydrant setups. Its janky, but I'll take the kill. Better opponents eventually figure my setups out, but its still surprising to me how few people know how PacMan's hydrant ledge-traps work.
There are some characters and situations which PacMan can setup a gimp. I've KO'd Donkey Kong after he's used his double-jump by just blocking their return path with repeated Hydrants. Ike / Chrom / Cloud can be KO'd if they lost their double-jump with a simple Fair->Fair ->double jump -> Fair Fair combo off stage.
At high tiers, opponents can KO you off of tilts (Pichu's FTilt), or off of a Tilt combo (Peach's DTilt -> FAir). PacMan has no easy kill combo that I'm aware of, so you're forced to do a hard read with a Smash attack of some kind. Good Hydrant placement can make reads easier (ex: Hydrant forces most opponents without reflectors off the ledge), but I'm not aware of a kill-option if the opponent does a jumping getup off the ledge. (Roll, quick-getup, and getup-attack can be predicted/punished by FSmash or DSmash. I can't think of a kill move if the opponent jumps however)