I really like alot of the ideas of DEI but the actual thing was really disapointing to me; ie campaign is super slow, troops roster is alot of duplicate units and bad balance.
Super slow is good for you
you say this because you are corrupted by native neck-breaking speed! Relax and enjoy as the seasons passes and you see empires crumbles around you. And watch your men fight it out instead of soldiers cutting through armors and shields like in movies!
On unit roster copy/paste troops, well there is some in DeI, but way less than in native... All of them have at least a different name/appearance (to represent the cultural difference), most of them have different special abilities (for example a unit who can hide in forest/scrubs, another who cannot but has the parthian shot) and also a different unit stat here and there to account for a small difference in strength or whatever, not to add that they have different recruitment cost/upkeep to incent or discourage from employing many of them.
The roster size has been nearly doubled for major factions and smaller factions which have been focused by DeI (some are still waiting to be overhauled), and new factions have been made playable with a vanilla-like roster (small and tasteless) + some interesting units.
Now, the balance is very different than in vanilla : they chose to keep it "historical", meaning that factions that did very well in history because of the strength of their army are represented by strong units.
Its no longer a every faction have lots of all-around units. Ahistorical units were removed, weak units/poorly represented units has been nerfed, some all-around stays and form the staple, and strong/key elements of faction have been buffed (elite units are army-capped so it stays limited).