And what is wrong with doing the previous raid? Like, old tier HC is very close to Normal diff of most recent raid, so it does make sense. Furthermore, if u keep ilvl jumps low you dont have huge power spike between tiers, like people going from 15k dps t1 raid, to 200k dps t3 raid. And on top of that the older content is still relevant instead of just completely replacing all pieces as soon as new raid arrives.
Moreover, if u make ilvls jump smaller, mythic gear is relevant for longer. Because now, even casuals who play only normal raids, are better geared as soon as new tier arrives, that guys who spend hours and hours on mythic raiding in previous tier.