I'd rather have Mitchell starting in center while Chourio is on the IL than Perkins - and frankly I'd rather have Lockridge starting there against a lefty than Perkins, too. Probably why Perkins started the year in AAA and not Mitchell. Burning Perkins' option upfront for the year sets the stage for a rotating cluster of 4th/5th OFs once Chourio does come back in a few weeks - and honestly the Brewers may have been thinking to use Perkins' option instead of burning one for Mitchell at the start of the year assuming Mitchell is more likely to get injured and go on the IL than Perkins.
Of those 3, I'd say Mitchell still has the best offensive upside should he stay healthy and get regular MLB at bats. I don't think anyone views him as a developmental prospect anymore as much as he's been an injury-plagued enigma who could still be a late bloomer if health cooperates. He's capable of a few monster 30/30 seasons with great plate discipline and GG caliber defense in center field even with high strikeout totals.