The most logical fix would be as Keir has suggested, as well as Nerfix.

Recruitment through pillaging with a reduction on the population loss and increased gold on pillaging because they were so effective.

Then they could have Turmoil in their provinces and in general it wouldn't matter since they don't require a castle to build their units outside of the Khan and elite.

If you could balance the numbers of recruitment and gold vs pillaging it would be an interesting twist on the entire theme/race.