I get that Blizzard wants to keep dungeons relevant throughout the expansion, but in doing this, they're making older raids irrelevant. There's no reason to run Emerald Nightmare or Trial of Valor now, because you can get higher ilvl gear in random heroics. Heck, there's not much reason to run Nighthold either, with Mythic dropping 885 baseline. You can breeze through low M+ to get 900 gear.
Just kinda seems like one of those unwinnable situations; either dungeons become irrelevant as the expac goes on, or raids become irrelevant.