Is there any thought that goes into Sage using Kardion on themself?

[Qeilos]

Is Kardia on a GCD then that breaks combos or something?

I dont think it matters. WHM isnt a healer to help you, AST isnt a healer to help you, SGE isnt a healer to help, SCH isnt a healer to help you. The best way to approach these games is your survivability is 100% your own responsibility and noone elses regardless whos in the game. WHM is frankly a better BLM than BLM is and I view them as such when I load in.