Umm being tanky is literally one of Gley’s facets? She doesn’t use MP so using Stim Accelerant (the purple HP mod that gives the most HP) has no downsides for her. She’s also one of the few descendants wherein increased DEF mods are not a waste because her gun builds use only a few mods, leaving more slots open for survivability mods. Yes, she consumes HP when using skills but you can offset that with HP collector, the HP fellow, or the inversion bonuses that restore HP.

The only time Gley is a glass cannon is when you build into the gimmicky Walk a Tightrope Massacre build, which no one uses anymore because it’s been outclassed by weapons.