They get a tremendous amount of data from their own telemetry and there were definitely enough people for that.
What may have hurt is if they didn’t have enough of the right kinds of people that are looking to break the game. Your average player isn’t going to find the niche exploits. With POE2 launching that week and that first day being pretty worthless with the PTR issues, they may not have seen enough or the kind of testing that breaks the game.
Even that wouldn’t be the end of the world because a lot of people who didn’t play the PTR will still play at season launch, but since they refuse to patch even serious bugs…yeah, something probably got through, yet again.