Pathfinder was to get around WotC dropping D&D 3.5. Paizo was started by veteran D&D writers to sell adventures, which they still do as adventure paths, rather than a system. When WotC updated to 4e, meaning no more print books that Paizo could reference in their adventures, Pathfinder was a way to print new 3.5e PHBs and Monster Manuals.

Paizo didn’t initially change much in PF1e. There were a few balance tweaks. The books were better laid out than 3.5. The players did the math on things like combat maneuvers in advance. In practice the game played pretty much the same, my groups jumped over seamlessly.

Having run and played both, I do think Pathfinder 2e is counterintuitively simpler in play than 5e D&D. 5e plays fluidly almost immediately, move and act. PF2e is pretty demanding for the first hour or three, the three action economy and Conditions ™ are an armful, and many players need to unlearn some D&D habits. Once a player has below average system mastery PF2e is as fluid as 5e. Beyond that PF2e shines. The rules scale better to complex scenarios, giving players more clear options of how they could act and giving the GM a better framework to figure out exactly what someone needs to roll. I also think it’s easier for players to go from average to good system mastery in Pathfinder, it’s mostly just learning how to optimize their character and learning more conditions and spells that work in the framework the player already understands.

For new players in session 1 D&D is simpler, in session 5 Pathfinder pulls even or maybe ahead, and in session 50 Pathfinder still sort of works where D&D falls apart.

PF2e character customization, though, is much more complicated, which some people like and others do not.