For a while, it was a popular theory that GEO would’ve been the first casting tank, casing barriers on themselves to reduce damage and having a way to nullify interruption.

I don’t think, given the lore we already have, that GEO “must” be a healer per say, because you can be creative with our existing lore or introduce a subset of Geomancers from Meracydia or something, but I also don’t feel it seems connected to the DPS role either.