It really feels like this part of the game is pretty obvious. If you can build cavalry- do it before all else.
Unit composition for me is two heroes , everything else riders or knights, maybe 1 other unit like a scout just in case.
Why would I bother building archers/snipers as a guardian when they pale to a rider, unless I lack the resources?
Paladins are nice if you have the logistics for non-commanders.
I'd argue that either horses need to be rarer, and/or non-cavalry needs to be buffed. Either that or give the SK some buff as hell pikemen.