Unironically this, and the show basically makes this point outright.
Abe is a complete simp for Cleo, and doesn't like Joan unless she's dressed up like a whore. He's also a huge asshole sometimes, like when he interprets JFK's sadness over Ponce de Leon's death as nothing but farming sympathy from Cleo. Note in that episode itself, it seemed like JFK actually WAS losing his mind out of grief for Ponce.
JFK, on the other hand, is a skirt-chaser, yeah. But he doesn't idolize and simp for the girls he tries to bang. And while Joan rejects his advances at first, he doesn't resent her for it, and actually seems to appreciate her for who she is.
Joan has a childhood crush on Abe, but in terms of JFK, actually complements him much better. If they were to actually date, she'd have the strength and self-respect to demand that he not go chasing after other girls. And JFK, for Joan, offers the happy-go-lucky, sunny outlook on life that Joan is lacking.
JFK and Joan unironically complement each other better.