I think the general consensus is that it improves security of the protocol, but obviously that won't matter much if the implementation gets something wrong or has worse security by itself.

Issues in the protocol itself would need all implementations to change, but issues in the implementation would obviously be isolated to one implementation. For something like Wireguard, I'd wager a guess that issues in the implementations are more common than issues in the protocol, at least at this stage.

If the implementation gets it wrong that can also be a sign of ambiguity in the protocol / standard and as such result in clarifications and an overall more well specified protocol