How hard do you think Mythic Antorus will be relative to Tomb of Sargeras?
Given that it is the final raid and it will be current content for a very long time, I anticipate that it will be tuned more difficult than Tomb of Sargeras to ensure that players are kept busy for as long as possible. Otherwise guilds will simply steamroll through it in a couple of months then unsubscribe for the next 10 months which is not in Blizzard's interest at all.