I still have difficulties to cope with the use of the term "mutual defense pact".
What we have ingame does not reflect this the slightest, but sure, it is somehow gameplay vs lore so it doesn't bother me too much.
However a mutual defense pact implies to me an equality between both parties, which have to be more or less independent from each other. It contrasts with the statement that the Khanid are now again a vassal of the Empire. In feudalism the vassal is the only one to pledge his services to his liege to benefit from his protection, it does not go both ways. It is how it works for the Ammatar Mandate, which is a protectorate vassal, and which also explains why the Mandate is currently not involved in the proxy war, unless the Empress call for her levies, which has yet to happen since only the Imperial Navy is now fighting in the war. The vassal families fleets are not involved, the same way that the Ammatar Fleet is not, and the Khanid Navy is also not involved.
A mutual protection pact would imply that the Khanid would have to answer military to come to the Empress help. I think it is a bad choice of words.