I'm only now getting a real feel for it having reached the island, since obviously having New Game + makes the earlier areas much easier.
Ammo is a pretty real concern, but it doesn't feel like you HAVE to skip enemies? It's more that if you play perfectly there should be just enough ammo. If you're sloppy it's going to tank you. Definitely avoid fighting Regenerators when possible though, and probably any optional bosses.
The hardest part of regular gameplay is the perfect parries, since you can't just spam L1 like in other difficulties. You really don't want to take those hits, honestly kiting is going to be preferred a lot of the time until you've really got it down.
The only part of Professional that is bullshit are the gimmick sections, they're pretty much terrible top to bottom.
https://twitter.com/OocWTC/status/1348011667976699904?s=19