Yes. Blame should be apportioned fairly to everyone getting things wrong. Not just pushed on one agent.Sony is also to blame for having multiple different explanations and for selling the game in locations that don't have access to PSN.
This is a unique scenario where the requirement was intended but it was disabled for 'technical reasons'.The other issue is how long this has been disabled for. Sony and the devs choose to disable this and make it optional. People bought the game while this was optional and are now past return periods. I don't buy MS games on steam so I don't know what was going on with Halo but did MS disable the need for a microsoft account for months and have contradictory information on it being optional and then choose to reimplement it ?
It's not the same situation. However, the information up front that some people claimed Sony didn't provide is the same across all games that require an additional registration somewhere. They were told, even if it wasn't implemented when they bought the game. It's akin to drivers ignoring Road Closed signs in the UK because often the road isn't closed at all. But if you then ignore such a sign and drive down a sink-hole, you were warned...Because only then would it be the same situation.
As for refund periods being past, I'm sure Valve will do right one way or another. There is definitely a share of responsibility on the shoulders of buyers who bought the game despite being told it needs a PSN account then finding they can't make a PSN account, not that any will admit to it, but I expect Sony and Valve to sort out something for those who can't create PSN accounts. It'd be very bad PR to take their money and not provide any means to actually register an account. This is a first time Sony has linked to a PSN account and clearly they messed it up and failed to realise their audience is very different on Steam and they don't have the same localised markets. As I say, ideally Valve will update Steam to require linked accounts before games needing other accounts are sold, certainly for some major players. Games like Last Epoch simply need one created on start. Oh, or Sony limits sale of the game to territories that PSN is available in. Although wasn't there an issue with regional pricing across Europe and Steam having to allow access to the same content to all EU states?