If you look into the far future, Medusa's second reprint isn't out yet, but probably will be in 1-2 months. If the weapon gains Assault/Pride from FLB, it'll be very good.
It's a bit of a gamble though, since it could also get something utterly useless like Crit or Ability. Well, Crit isn't entirely useless, but I'm not a fan of it since if you're using elemental advantage, then you're usually in a good spot anyway.
So, if you can run Ultimates, I do recommend maxing Medusa's weapon just for the potentially great FLB.