**hiding good math**
Copperbell Mines, GLA, 395 HP, Naked, No Protect
Minimum coblyn damage: 50
Maximum coblyn damage: 54
Coblyn hits to kill tank: 8-8
Copperbell Mines, GLA, 395 HP, Naked, With Protect
Minimum coblyn damage: 50
Maximum coblyn damage: 55
Coblyn hits to kill tank: 8-8
Difference in damage between -Protect and +Protect: None
Effect of protect on tank survivability: None
Copperbell Mines, PLD, 629 HP, Gear Sync, No Protect
Minimum coblyn damage: 35
Maximum coblyn damage: 38
Coblyn hits to kill tank: 17-18
Copperbell Mines, PLD, 629 HP, Gear Sync, With Protect
Minimum coblyn damage: 32
Maximum coblyn damage: 35
Coblyn hits to kill tank: 18-20
Difference in damage between -Protect and +Protect: 3 damage (10%)
Effect of protect on tank survivability: 0-2 hits
Since tanks in Sastasha/Tam-tara/Copperbell will fall somewhere between these two scenarios, we can conclude that Protect will buy a tank between 0 and 2 extra hits.
The lower the tank's defense and HP, the closer this will be to 0.
The more damage a mob does per attack, the closer this will be to 0. Consider for example, a mob that hits a 629HP tank for 100 damage per hit. It can kill the tank with seven 100dmg hits, and it would still take seven hits if the damage were reduced as much as 10%.
Meanwhile, an AST with gear sync in Sastasha goes from dealing 37-40 damage per Malefic to 68-72, a gain of 80%-84%.
This is not negligible. Expect the damage gain to increase with higher syncks.
Supporting screenshots
Copperbell Mines, GLA, 395 HP, Naked, No Protect
Copperbell Mines, GLA, 395 HP, Naked, With Protect
Copperbell Mines, PLD, 629 HP, Gear Sync, No Protect
Copperbell Mines, PLD, 629 HP, Gear Sync, With Protect
[u]Sastasha, AST, Gear Sync[u]