So basically people consider AST to be the Time Mage because it has.... Time Dilatation and Gravity and can sometime give haste?
There's a bit more to Time Mage than Gravity and Haste.

I'm not trying to deny the fact that AST do has some Time Magic, but that's it. It just has "some".

The AST doesn't feel like a Time Mage at all. I can't even recall a single game where Time Mage was a considered a healer. It's always been an offensive support with access to a regain spell at most.

Time Mage has too much of a strong identity to be ignored by SE. Like other "core" job such as Blue Mage for instance, it just a matter of time before they include it in the game.