It just sounds like your bad at using alter time…
Here is how I used it in AtDH:
Gnarlroot: Controlled Burn alter time, shimmer out, then alter back in letting you save your shimmer charge for the frontal if needed or P2 to get to and from soaks faster
Igira: Spears (this one is just for dmg, but still better than a cheat death since I can use alter time on every or every other spear)
Volcoross: Serpent’s Fury Pop alter time every time he uses this ability which is great completely negating dmg from the mechanic and letting me save other defensives for the coiling flames soak and normal soak
Council: Poison Javelin alter time shimmer out then alter back in so nice! Wasting 2 shimmers here would be such a waste considering how much is going on in this fight it is so dam hectic that every shimmer counts! (dodging/getting into the charge, dodging swirlies, dodging frontal, repositioning depending on bosses jumping/teleporting and pool locations…)
Larodar: Raging Inferno (P1) and Consuming Flame (Intermission) amazing here since he deals dmg for an extended period of time w/ the intermission being 16 seconds! One of the strongest defensives for dealing w/ damage over time effects! Ashen Devastation in P2 I get this thing I run out of the raid into the lava as far as I can and alter back to raid full health negating tones of dmg from the raid group.
Nymue: Weaver’s Burden this thing needs to be run out far from the group. I curse this boss so much when I get this thing on me and I don’t have alter time up… Another super hectic boss w/ frontals on the add, lines to dodge, and a bunch of soaks to reposition to that every shimmer counts and using alter time to bring the debuff out is massive considering I teleport back like 3 shimmer lengths!
Smolderon: Every single intermission this thing is amazing! I use this + 2 shimmer charges in every intermission to maximize damage!
Tindral: Dispells! These things hurt so badly so be able to alter time, shimmer out, get a dispel, then alter back full health is a massive help to you healers who don’t have to worry about ST healing you in this hectic as hell fight
Fyrak: Circles to bring to the edge in P1, and seeds in final phase like this is one of the most skill expressive times you can use alter time from the pushback, bringing circles around, juggling seeds…
Alter time is such a sick ability and in no world would I want to trade it for a cheat death!
All 3 mage specs are insanely tanky I never feel at risk of dying playing any of the three specs from some sort of unavoidable dmg.
In 6.5 of the 9 bosses in Amirdrassil I was using alter time primarily for movement. (I gave Larodar half credit since P1 I use alter for dmg negation over long periods of time P2 for movement)