Well ... adepts are a slower and less reliable unit-class, but they are supposed to be used by skilled players.
I was able to play several Shieam games while having nothing more than adepts. Especially so if I started next to the Broken Sepulcher. You would only get death magic and combat promotions (as well as mobility 1 eventually). Only attack with skeletons. Your skeleton horde will slowly weaken them ... and while your building adepts, your teching for sorcery. Once you have sorcery, you tech for the Veil.
Even before sorcery, your always looking to expand over mana nodes to make your (eventual) spectres more powerful. spectres were 3 str +1 death affinity. You started out with 1 death mana, the Sepulcher gave you another ... just three more and your mages could have 8 strength Spectres. Include Veil and that army could be guarded by Rosier the Fallen and any Disease Corpse hoards you are inclined to train.
If you play as the Malakim, go for an altar victory, and play defensively (as well as spreading at least 2 religions) ... you can build ready made-mages in the late-game. (although relative late-game, with enough shortcuts you can get it in most people's mid-game. It requires teching Righteousness for the ALtar VI, as well as having Veil in your altar city, and building a temple of the veil. As well as having Sorcery. Another benefit to this strategy is having fire mana acessible, since fire mages are the best kind of mage to produce in large numbers. Build Savants, which can upgrade into mages at level 4. with Desert Shrine + Altar VI, they should be built with 17 experience. This is enough to get to level 4 (for mages) and then buy two points of magic ... enough for Fire II (fireballs).
Of course, these mages (if using my ROK->Veil->Order strategy) will be defended by HighLevel Paladins and hoards of crusaders.
also, if you happen to be using the Aristofarm economy, a short bypass to Feudalism and aquisition of horses will allow you to build the very Utility Royal Guard unit, to help protect from assasins. They way guardsmen works in base FFH is that having a unit with guardian will allow the strongest unit to defend vs assasisn. In this case, it would be the high-level Paladins.