This is on VH Campaign with the Irish Vikings.
I have 3 provinces in Ireland plus the Isle of Man. My income is almost 4K per turn despite my army cost being almost 2K. The only limitation on me raising more men is Food, which has always been the bottleneck throughout the entire campaign. All my building decisions prioritize food, not gold income and I still have too much gold with too little food.
As a result, my armies are mostly Retinue troops. I have no incentive to train Levy troops because they cost the same food as Retinue.
The solution I think is not to lower the gold income (as high level buildings are so expensive) but to adjust food costs.
Retinue and Elite troops should cost MORE FOOD than Levy troops. Cavalry should cost more than Infantry.
Here's my proposal:
Levy Infantry: 5 food
Levy Cavalry: 10 food
Retinue Infantry: 10 food
Retinue Cavalry: 20 food
Elite Infantry: 15 food
Elite Cavalry: 30 food
This gives the player some incentive to actually train levies rather than going all Retinue/Elite level.
It also makes more sense historically as Retinues would be full time soldiers and thus contribute nothing to agriculture. They would also demand more meat and have their own servants/family/clients to feed, so they should cost more food.
Cavalry costing more food is a no-brainer.