This is wrong on so many levels.
First off, you have this “5G” which supposedly is capable of almost a gigabit per second (as opposed to 150Mbps or so on LTE) and yet the data cap is lower than the one on the inferior protocol?
Second, how are those data caps managed? What happens if you run out of your 5G cap? Does it kick you off back to LTE? Do you stay on 5G but get throttled to LTE-like speeds (which wouldn’t be that bad actually - given 5G’s maximum is huge, you have more chance to get the max LTE speed over 5G than on real LTE since 5G has more bandwidth to cope with errors & such). Do you get throttled to some stupid speed like 2Mbps? (something tells me it’s the latter)
Finally, just why? Why bother with such a plan at all? Having this 5G is basically useless on it (if you’re lucky enough to get a signal, you’ll blow through your cap in minutes and then the above problems will apply) and only adds confusion and no doubt will decrease consumer satisfaction (sure, it’s technically their fault for buying such an useless plan and not understanding the terms, but realistically, do you expect the average user to understand all this and keep it in mind while using their phone?).
Good on Three for making it a seamless, incremental upgrade. Given 5G’s (designed) flakiness it’s expected that you’d be switching between 5G and LTE every few seconds depending on how you walk and hold your phone (hopefully handover is instant) so having separate data caps is going to be a nightmare to manage for the customer.