I don’t believe it’s meant to be like “You can only unlock one even though you have 160 tokens.” Sounds like their trying to say that you can only earn enough tokens per season for one.
It would be really dumb of them to not allow people to buy both, seeing as some of those would inevitably be made by people who bought more tokens because they didn’t have enough for both.
You are reading it wrong. You get enough prisms from the Battle Pass to get either a mythic skin or a weapon skin. That is what they are referring to. You can still use old prisms to get whatever you want or even both but the BP will only give you enough for one.
It’s not really gatekeeping, but more paywalling.
You can earn enough tokens for 1 item through the battlepass, but you’d have to either wait until the next season to earn more, or just buy more through the store. Not really a surprise that this is the route they went to be honest