It's more tedious and time-consuming than difficult. Unless you quickly upgrade your units.

No skilled player will spend time upgrading units in the late game (unless there's a mentor to help remove all that clutter later). Playing will become genuinely difficult, leading to losses on neutral territories. In this situation, you shouldn't focus on units but rather on quickly developing your Necropolis - only then will you be able to avoid losses from various archers and mages. It seems you've just gathered random information from forums and are now trying to present it in a disorganized way. Learn how to play first, instead of pretending to be knowledgeable about perks and skills.