This is false. There are not infinite rewards. It shows you have no understanding of math. No matter how much you want to posit some ridiculous 24/7 game playing you still cannot get infinite rewards.
Pretending everyone can play for 168 hours without stopping is a ridiculous laughable statement that deserves ridicule. But it still wouldn’t get you infinite rewards as there is a literal time cap on a week, you cannot make more hours in a week than exist already. You cannot run an infinite amount of dungeons in 168 hours.
Ignoring that, the dungeon drops do not reward mythic gear. Only the vault rewards mythic gear, and it’s only the base level mythic gear it does not scale up to the max level mythic gear. Valor is always capped during the meaningful part of the season, so even the pieces you can upgrade will not suddenly be all upgraded in a week or even a month.
You can argue all you want that M15’s have rewards far better than their difficultly. But that isn’t the same as infinite rewards which is a 100% false statement.