Arrowhead isn’t free of guilt in this, but Sony and Valve should have both done a much better job at making this clear to players earlier on, since they’re in charge of marketing/sales on PC.

Well they kinda did. When you first launched the game it did say that you need a PSN account to play. I know this because that's when I learned PSN isn't available in my country. But you were able to skip it and after skipping you never saw this notification again. Valve also has it on the store page "Requires 3rd-Party Account: PlayStation Network (Supports Linking to Steam Account)", but nobody reads those little notices. I don't blame anyone for missing that information, especially since not linking PSN accounts has not affected the game for months.

And if you want a really fun fact. Web archive link because I imagine Sony is going to change it, but on the Playstation website they explicitly state "Signing in to PSN is optional when playing a PlayStation game on PC.".

I'm not going to to anything hasty. I hope Sony walks it back because I do enjoy the game, but if by June nothing has changed I will ask a refund from Valve because I'll literally be unable to play the game, unless I go against PSN ToS. I have no problem getting on the FUCK SONY train once they've left me no other choice.