Magus is for sure a non-bo with the mana bases of the best human decks from recent years (Storm's Humans that won in Spain spring to mind here.), but a couple questions spring to my mind at least.

Firstly, could you just jam a couple Magus into some version of Humans as a sort of uncounterable (off of Cavern), Armageddon-like effect to just end games where you have already played out a Thalia, into Mantis Rider, into Reflector Mage and then Magus is the cherry on top that never lets them replay the Smasher you just put back in their hand.... ? Maybe? I kinda doubt this would work myself... but maybe some slightly redder version of humans with Harsh Mentor is out there where Magus is a capstone sort of lock piece. The destroying your own manabase does seem like a problem though.

Secondly, is there a much much redder version of Humans out there? Something more like Kurt Crane's Moons deck from NAChamps (https://www.mtggoldfish.com/deck/503260#online)

Assuming that Harsh Mentor is good, I actually think that something along these lines with 4 Magus, 4Harsh, and 2-4 Blood Moon might be pretty tough, since the opponent will be dealing with a Magus or a Harsh nearly all the time, and will be faces with crazy problems like having to try to remove Magus, so that a Flooded Strand can become not a Mountain, and instead become a fetchland that costs 3 life to use. If a second Harsh comes down, it now costs 5, and at that point shouldn't they just be in such an impossible situation that there is no getting out? I'm also optimistic about this angle, since Magus seems great against both Eldrazi (which I think is the worst matchup for Humans) and Mentor, while Harsh seems great against Shops. Now just add some number of Eidolons and you have multiple, on-color, mainboard answers for a huge chunk of the metagame. (56% of top 8 decks in the last year, going by mtgtop8)