Quoting what I said in this thread:

Quote Originally Posted by Inferiae View Post
Because it's a lot easier to sync when you also sync the skills. Here's an example:


Imagine two BRDs, one level 60 and one level 50, in Sastasha. Let's sync them down to level 18, but not sync the skills.

The level 60 has access to traited DoTs, two DoTs, Empyreal Arrow, Sidewinder, Wanderer's Minuet, all his cooldowns. Even after being synced down to level 18 attributes, there'd be need to adjust every single skill potency to meet the standards for Sastasha.
Level 50 doesn't have EA or WM, but has access to all his cooldowns too, and traited DoTs. So, we'd need to lower his potency too, but not the same amount as the level 60 BRD, because it doesn't have the high potency skills the level 60 has, so the rotation is different, and potency per second is different.

Now imagine that for every job and every level in between the dungeon level and 60. It is much more practical to sync the skills too, so every one is in the same standard.