Developing a cultivation realms will be harder in xianxia because there a comprehension elements the cultivators reach a certain level, higher the realm the more complicated it will be. In xuanhuan in my knowledge it just like basic leveling system, to reaching higher realm pill/ rare treasure is usually good enough
I think you should test this by increasing age limit after BT a bottle neck, so people can reach lv 10 condentation eventually, and by then u just add a tribulation when peeps try to BT to foundation, and kill em instantly because heavens(you) not allows that XD