I suppose OP forgot that he had psiStrengthEval option enabled. With vanilla options, there is no issue.
No. The actual reason was even more embarassing than that!
For my AI-tests I almost exculsively played the quick-battles.
And while I restricted myself to early-game-equipment, in quick-battle you obviously have everything researched and everyone tested because otherwise you wouldn't know who your Psi-soldiers are in case you decide to use psi-stuff.
I just somehow assumed that the equipment-level is reminiscent for the tech available to me. Which in hindsight is highly questionable.
So, sorry for the false alarm.