You can get it in later expansions… I can go do Mythic Vault of Incarnates to get Mythic Vault of Incarnates gear.
In my opinion, if you want Mythic Mana Forge Omega rewards then you should have to do Mythic Mana Forge Omega.
If you want pvp elite rewards then you need to get the appropriate rating for it.
I think being a delve player and expecting equal access to all the same rewards as Mythic raiders is a bit entitled