Marvel de-ages the real actors, while Lucasfilm are using stand-ins. The results are clear when the best use of this was Kurt Russell in GOTG2 i.e. his makeup was done first to help the effect.

The Dark Troopers were cool but now they’ve had their limitations shown it needs something new. You can’t have an enemy that is nearly invincible until a lightsaber arrives, there’s no room for a style of battle scene in between. I expect they will explore whatever the bodies were that rejected Grogu’s blood in Chapter 12.