Since u10 should be a more appealing and interesting in the way that u9 is compared to u8, why not differentiate bronze reward of u8 and u9 from u10?

Thus making u10 more likely to be farmed instead of ignored (because if we get the option to ignore a harder world that brings no relevant difference from its lower difficulty we will surely avoid going for the hardest) make "old bronze reward" exclusive of u8-9 and "new bronze reward" u10 exclusive.