I managed 2 of the three challenges of my class. For back round I have been a CE raider for over a decade roughly around world 300 with spikes up and down that over the years and a middling pvp rating of 2k depending on expansion. I completed 36/36 legion mage tower with several classes being done during its launch patch.
I don't know how many of these fights are being done in their intended way. I did the Twins as MM and while caught off guard by the enrage being a instant wipe and the hands dying extremely easy it became clear they changed the encounter to be about kiting. Fair enough I managed to kill rast while his bother was still alive.
BM I am willing to say that without a twink build can no be completed as currently intended. I managed to beat it after about three hours by using the WoD tanking trinket to endure the bosses dmg long enough to effectively kill the worm and feltotem at the same time. The worm has to die first as the enrage will simply kill you outright. The class isn't designed to sustain itself for the numbers the boss has and given that my kill clocked in at just over 13mins I can't say this was the intended method to do it.
The old mage tower was league easier even at launch the new one in many cases just feels untested. You can lose from doing everything correctly and I can't agree with that being good design.
If you completed the old mage tower in legion I would of been comfortable trailing you half way through mythic on that alone (during launch patch). If you managed to clear all challenges without twink gear I would be comfortable trialing you in mythic slyvannas.