I wouldn't have any concerns at all about the PS5 becoming obsolete any time remotely soon. The PS4 is still getting numerous recent AAA games like Hogwarts Legacy and God of War Ragnarök, plus upcoming games like Resident Evil 4 Remake and Assassin's Creed Mirage. With the PS4 (released in 2013) still getting that level of support in 2023, the PS5 will be alright until at least 2030 probably a little more.

Digital download games go on sale on console quite regularly these days, there's a big January Sale going on on the PS4 & PS5 PlayStation Store at the same time you posted this. Maybe sales were less frequent on the PS3 PlayStation Store, but things have changed since then. Physical games on console are also still very much around, so unless you bought a PS5 Digital Edition or Xbox Series S you do have more than one place to buy games from on console.

Wait and see how the game runs on Switch. "Exclusive" quests to one platform in these situations aren't worth mentioning, when it's only on one platform they can't do anything that matters to the story anyway in "exclusive quests". I've played games on PS3 where things like "60 minutes exclusive gameplay only on PlayStation" was just a minor side mission outside of the main story. Not bad, but not worth buying a whole other console over.