I suggested the same, but also want Masteries displayed on the loading screen. (That’s before I played on PTR and I wasn’t aware Prestige is shown at the bottom-right in-game.) I suppose in-game is okay but show masteries somewhere and not require a replay analysis script to see it.
Ideally, you’d be able to choose your Mastery (like on MM maps) and your Prestige after the mission loads, and you know what mutations you have. I guess we can’t do it after knowing the enemy comp since that requires getting attacked and hit by the enemy at least once - but that really does change things for some CO’s. (Raynor’s beefed up bio units and no mules seems pointless against mech; or against Immortal, Reaver, Disruptor, for example.)