Your reasoning still doesn't change the fact that Khabib is significantly a higher ranked fighter than Diego. If we are going by popularity, then yes, Diego is higher ranked than Khabib.
Also, I dont see anything wrong with Michael Johnson getting a shot at Khabib. Yes, he is only on a 2 fight win streak but he impressively defeated 2 UFC journeymen (Lauzon, Tibau), both in dominating fashion.
On a side note, remember when UFC were trying to sign Fedor, part of the negotiation was UFC had to sign M-1 talent, which would have significantly bolstered the UFC's Eastern European roster, but that all fell through. It would have helped UFC enter the Russian market.
Lately the UFC has been signing quite a few Russian based fighters, mainly Dagestanis (Khabib, Rustam Khabilov, Mairbek Taisumov, Adlan Amagov, Ali Bagautinov, Nikita Krylov, Rashid Magomedov, Zubair Tuhugov, Omari Akhmedov). If the UFC can come to terms with Mahmed Khalidov, (the only big Russian based fighter remaining), Uzbeki, Ukrainian, Chechian fighters, their roster would add even more name value, and their plans to break into the Russian market can be coming sooner than later, as Russia would love to see their people fighting at home.