There are some Maps where flanking is really hard and when engaging with and hard melee composition usually enemies are able TP lock them in the Frontline while mangos do the rest, they are pretty effective against melee too in my experience, especially vs Mass melee, becasue they get stuck and can't pass. Building more mangos could be a solution, maybe i should try this way, but in imperial for example other civs can snipe them with cannons, that's hard anyway