Some of the level-up unlocks in treasure wars (and every game) are hubtitles and avatars, meaning that when you prestige and level up to a point where you would usually get a global cosmetic, you get nothing. Heres my suggestion.
Prestige Exclusive unlocks
There would be a new section in the treasure wars locker, prestige rewards. In the locker, there will be 18 brand new unlocks exclusive to prestiges.
Unlock (x) would be rewarded at level (x) but only to people that are at least prestige (x).
The unlocks would be in place of the global cosmetics, and would be distributed evenly throughout prestiges.