The problem of flails is that they have very particular physics which is not really manageable by a game server of that size. They could just make it a simple animations but then it would lose it's very big advantage of being on a chain (goes around shield easily)

Flails were not on long chains as you see it in movies. The chain connecting weight with the handle usually consisted of 2-3 rings.

Human culture is very diverse, when you study carefully, you will see that medieval geometry dash meltdown people are very talented and creative.