In this case, I think the cases where it was extremely valuable are rare enough that it's not bad game design to remove it. We got by just fine without it before Stormblood. We'll get by without it now. For it to actually be worth leaving in the game, it would have to be made significantly better than it is. Also keep in mind that it wasn't BLM specific. It was magical DPS, and it was useless to RDM once they got Vercure, and useless to SMN (though maybe less useless now, thinking about it).