Further research strongly suggests that garuda stats are snapshotted when summoned (like wow temporal pet in the WotLK and Cata)

I'm now examining whether the snapshotted stats are affected not only by gears but also by temporal buffs. At this time, I suppose it seems that the snapshotted stats are contributed only from gears.

Maybe, spellspeed things have to be reexamined... I remember I did not resummon garuda during the tests.