In my opinion a flat damage increase that has no interaction with any of the spec mechanics should never be the most desired stat. The fact that right now it is is just a proof that something is not quite right with how the specs work.
Mostly the specs got worse when it comes to stat interaction.
Take a look at assassination for example...
- Rupture is dominating the spec's damage, but rupture is neither affected by haste or mastery.
- Our mastery only affects one aspect of our damage and even if you try to get as much mastery as possible... rupture will still be the top of the list.
- Haste always had low value for assassination, the way to speed up the spec is with critical strike since mutilate critical strikes provides more combo points.
- Having more combo points provides more envenom windows... do you remember what i said about poison damage and our mastery? yeah, that will keep a constant damage, but the main star on stage will still be rupture.
- Versatility will increase your rupture damage. It will also increase your poison damage. It will also increase your mutilate critical strikes damage. It will increase all damage!
You can see similar tendencies with the other two specs. Versatility got better because the spec's main damaging abilities have little to 0 interaction with the other stats.
Edit: I know it seems strange, but you'll get used to it. Versatility never was a bad stat, just a boring one.