the overall (strategic) "Tier" of any such character who accomplished such a creation feat should indeed be Star / Universe level (or whatever else they created)

but creation feats should not automatically result in "Attack Potency" or "Destructive Power" being upgraded to that same level

There are several (likely nigh-omnipotent) characters in fiction who have created multiverses, but they still have the body and "attack power" of only a bunny-like creature or they can be fought equally by a 10-years old boy and his pets