For something that has had all its assets in the game since launch (ie. carbuncles), not being able to do this for so long is really a bad joke by now. They could easily have slapped an additional skill "Summon Carbuncle" on SMN and call it a day ages ago, it would have been an ugly and rough stitchwork of solution, but at least we would have it already. Instead of - whatever else they're trying to do that obviously seems way too complicated and/or low-priority to pull off.
