Let's look at facts:
HM: 26, JS: 25
Average ratings from world cup: HM 8.0, JS 8.5 (
https://www.bbc.com/sport/football/44834111 )
Most CB pairs has an alpha defender, the director and the one that has the ball the most. Clearly, Stones was that defender in the WC. I will admit I have not followed them much this past campaign and I know Stones suffered from injuries. Again, from the WC I thought Stones was the better CB and has the bigger upside.
It would not be crazy to let City buy HM for 80 mil and we buy Stones for 50 mil, and soon Stones is considered the better CB.
I like Maguire, I just don't ever see him being on par with Vidic and Ferdinand. Stones could possibly get there.