You got it in that you can only buy gem’s you’ve aquired with that character, but the flip side is that gems are BOA and as such you can just ship them off to your alts.
Use all of them.
That makes sense. I don’t do stuff like that too often this season so I just stuck to single target focus, but maybe something to consider for M+ next season.
…I just really want that mount, so back to the good ol’ grind.