That was pointed many times before.
Hordes are not supposed to be weaklings. Hordes are not mendicants.
C.A. and many "survival horror" play style fans do not understand, what hordes are about.
Why ask for money every few turns when they just should give automatic tribute via vassalage. This is just additional micromanagement tax.
And these people do not understand what hordes are.
Obviously most of them never took a good history lessons on historical hordes.
They are always huge power, at least major ones. They, translated into game, can support no less troops than usual nations/factions. Endless tides of savage warriors - is what hordes about. Not some roaming homeless beggars.
They autonomously can support big armies with themselves. They produce weapons, clothes, dishes, tools they need, and homes, trade - all with themselves. Their settlements are just mobile. But are the same money making, economy-making infrastructure.
Second, about vassalage. Hordes had vassals for constant money stream, bread stream, and military aid.
They just uses their vassals for "sucking" their economy and vassal military for own power.
Scythians, sarmatians, huns, rechenegs, khazars, polovtsy, so-called mongolian hordes, different tatar tribes, and other, - all were the same in the northern black see steps, before, at and after (Kievan) Rus times. Many hordes lived there and most asian hordes were migrating though this area to Europe.
Hordes always have big, strong military power, or they do not exist. And many times they take big part of resources from their vassals. Mostly food and money. Plus, loyal vassals support them in wars.
That is just historical rule.
Why "warhammer" hordes suffer so much? Why are they so, so weak?
Fantasy hordes should not be inferior and less frightening, in A.I. or players hands, than the real ones.
They need income building chain in each stack. And take bigger portion of vassals income every turn, without begging them for money via diplomacy.
Vassal should have his income reduced, but build and recruit his own forces. And hordes should have same military might when owning same territory, as settlements factions. 40 provinces - 12 strong stacks. Not 2. All must be like high elves, dark elves, lizardmen, etc. You own huge empire - you are unstoppable.