Banner are the clear bottleneck so that ULs aren't completed too fast in the beginning; there is a clear way to make them with the exchange, 2 a day (because of the cooldown) isn't so bad.
Excess shields and badges can be exchanged for tokens to fund that 24 cooldown set + weekly event upgrade
Excess 90s can be used in other sets or as exchange food
Everything has uses, its well set up. ~14 Banners a week from the set + any random drops means you can do a UL every two weeks AT FIRST. Legends was similarly hard in the beginning.
I think its set up quite well.