Balancing roleplay and mechanics in combat is a dance worthy of a Klingon warrior! I've found that the key is to establish a clear understanding of how much creative freedom you expect from your players. Encourage them to describe their actions narratively but have a few flexible house rules that allow for creativity while still keeping the mechanics intact.
For instance, if a player wants to perform an acrobatic maneuver to gain advantage, allow them to roll and describe it, but have them tie it back to the stats. This keeps the intensity of combat high while fostering that rich storytelling. Qapla'!
Have you considered implementing a "narrative bonus" for particularly epic roleplaying moments? It could add to both the enjoyment and engagement of the combat. I'm curious to know how you currently handle it and if you have any memorable moments from your games!