I’m seeing a lot of variance in the ratios. Some flails have longer handles, some have short. Some have chains as long or longer than the handle, some have almost non-existent chains. What are the advantages and disadvantages of various handle and chain lengths, and is there an “optimal” ratio?
No that’s generally not the case. A sword is still going to be more effective against armor than a mace. Even a fully armored soldier has plenty of gaps to go for.
Maces were never as widely adopted as swords, even during to height of armor adoption.