Well the fact that you even admit in passing mythic+ doesn't solve the difficulty issues your looking for a solution too should be enough for you to rethink the issue.
Mythic+ is a solution for people to gear alternatively to mythic raids they can't do for whatever logistical reason. Adopting it for the purpose of more difficult dungeons is folly.
And as far as a line of thinking to not get anything done, really? I gave you your difficulty solution already. The problem is predictability, the solution is unpredictability.
