On that thread about non-martials having a rough time getting new weapon proficiencies which scales past Trained, had me thinking of the ①titular question, and the following derivative:
②Is having multiple martial classes with strict niche protections on the availability of individual fighting styles worth it for the game?
The fact that when another game, the often ill-spoken 4th Edition of Big D, divided classes into power sources, had a single Martial source manage to cover all classes that weren't Arcane, Divine, Primal, Psionic (4E's probably-equivalent to PF2's Occult), and Shadow, also cements this personal suspicion that weapon based fighting as a whole being divided among classes might be harmful to both the martials themselves and spellcasters.
P.S. Just in case, while the question may seem adversarial against martials, I actually prefer them to spellcasters (due to underdogma, I admit though).