Honestly, they are doing many things right that paradox does wrong in their games, like meaningful buildings or not having magic buttons
When you build a city in Attila you really need to look for food, sanitation, public order, unit unlocks, etc.. When you build a province in EU4 you decide whether you want a fort there and then spam money buildings. I:R goes further in the wrong direction, by having only 4 buildings. More buildings, less slots like in total war makes for meaningful choices.
Magic buttons are cancer. If you manage to let your public order go down to -100 a province will revolt, there's no magic harsh treatment button that increases public order
Same for religion. I:R should just drop the idea of the magic button to convert pops and simply steal the religion system from Attila.
I also like the choice that comes with tech trees rather than linear tech paths
Paradox makes good games that are a lot of fun, but their obsession with "magic mana from the sky" really hurts them.