50+ hours clocked 100% solo, Gunslinger (so no auto-revive as some other classes have), Veteran difficulty, haven't encountered a boss I couldn't deal with though a few had me cursing them out. Obviously this is highly skill dependant but I'm very good at this thing called video games lol, actually beat a World Boss yesterday and took zero damage.
I'd argue solo is the *best* way to play, much more immersive, take your time to explore and drink in the fantastic world(s) that has been created, read through the excellent lore entries, speak thoroughly with every wonderfully written/voiced NPC (NPC's at the home base are the weakest, everyone else is superb). Also, performance on Balanced mode on PS5 is rock solid solo, rarely dropping, that's genuinely been my experience