So, there is no way to get 100% secrets on E3M6, without having to enter the secret level? That really adds up lots of time, cuz Warrens is not a fast map for UVMax.

Correct. You'll have to submit any UV max runs on that map to the secret exit category. We can't remove the category because of the way the leaderboard is set up, so just ignore it's existence and submit it to the secret exit category.