I mean, there is a very simple way they can fix this. Upon reaching the level cap for the expansion reach 24 man released in, lock Alliance Roulette unless your ilvl meets the minimum requirement for the third installment. For example sake, you have access to the roulette from 50-59 provided you have unlocked Crystal Tower and completed all three. However, once you reach 60, you lose access to the Alliance Roulette until you reach ilvl 235 and complete all three City of Mhach raids. This happens again upon going from 69 to 70.

And before anyone comments they can't do this. Expert Roulette already does. You currently have to be i410 and have all three dungeons unlocked or you can't queue. So they could very easily do it with Alliance, and just may if this continues because it makes queue times for the older raids extremely long.