Personally, I think Noah's departure made Mag a priority signing. While Mag ain't the shooter Noah is, & obviously ain't as tall — I HIGHLY doubt Noah would beat Mag out for a solid role at either the 3 or the 4. One of Noah's best traits was his speed & quickness for his height. But in neither of those things is he even comparable to an athlete like Mag.
Mag also gives us the explosiveness tht Noah didn't. (Which was a big reason --I think-- why Richie stole more than a few of Noah's minutes at the 4 by late conf play. Lacking explosiveness at the 4 is a tough deal vs Big12 competition.)