thing is, magic fencers would be competing against ninjas, not princesses. they're used more for their range than 'magic dmg on activation duelist'
I'd CR/SU the sybilla prime myself, but doesnt mean that having 2-3 duelist isn't necessary, most notably the somewhat recent 2nd G tier map in Horus event. (3 liches) and the 8th map (also 3 liches)