Why Didn’t the Emperor Use Thunder Warriors Against Xenos Instead of Wiping Them Out?

The Thunder Warriors were brutal and flawed but undeniably powerful, reportedly capable of taking on multiple Astartes in combat. Instead of sending them to fight xenos or Chaos, the Emperor orchestrated their brutal extermination at Mount Ararat. Why?

Their genetic flaws weren’t ideal, but they could have been fixed or managed for a few hundred years—long enough to be useful during the Great Crusade.

They were faster and easier to produce compared to Astartes, relying on adult veterans rather than long training pipelines.

Their raw combat strength and resistance to the Warp could’ve made them a powerful disposable force against xenos and Chaos.

Even without the Mechanicus, the Emperor managed to create legions of them during the Unification Wars. Couldn’t this production have continued alongside the Astartes?

Was their instability really so dangerous that the Emperor had no choice but to kill them, or was it more about consolidating control and ideology? Why not use them as a temporary force while perfecting the Astartes?