Not sure if he's worth a promotion just for it, per se, but yeah, I tend to base most my decisions on the upcoming arena heroes and focus on a core trio of units. He can replace Jaffar temporarily but I think him, or something like him, may be a necessity for sniping units getting out of line. Michalis is more of a mobile physical tank so while he shares a lot with what Eirika is bringing, her buff utility is pretty hard to give up and Y!Tiki is the closest to a mage tank in that setup, though worth noting I expect a lot of Spring Lucina in the coming weeks to lower her value somewhat.