Not by much, i guess.
Mystic boost have 2 good things about it, renewal every turn and nullifying adaptive damage, if second isn't needed i don't see much value in Mythic boost on Chrom here, just keep renewal.
If you use chrom for healing and dragon check only, then keep renewal because mystic boost health only activates if you fight. If you use chrom to battle often, then use mystic boost.
Plus, only time Chrom should be concerned about adaptive damage is if his opponent a) runs Sorcery Blade and has a mage nearby, or b) is a Felicia with plates. Odds are good you'll have someone else deal with those units if you encounter them.
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