But it's pointless since it's only useful for leveling Because it is unusable in instances or warzones, i think

I have legacy level 40 currently. I have all 8 adv. classes at level 50, yes. But i really want to know, what exactly is the point of having that high legacy level and the same expensive unlocks cost? 'cause as of now, they aren't really convenient to me, more like completely useless... I think legacy level should atleast reduce unlocks cost by some percent... or maybe i'm wrong and there is some reason for all this?