Leicester are misguided to take Coutinho fee as the benchmark for Mahrez valuation; similarities are goals from outside the box, otherwise Coutinho brings plenty more meat to the table. Mahrez useful in a specific scenario - quick counters, which I am guessing is the reason Pep wants him, would be impressive on one wing and Sane on the other wing. We don't need Coutinho type skills - plenty of those at City already. And given < 5 teams attack us in PL, Mahrez would only be a squad player. Could permanently replace Sterling when we play Liverpool, also good against Arsenal, Spurs and that's it really.
Stats showing Mahrez has more goals/assists than Coutinho are not that useful really - Sterling has more goals than KDB yet it's indisputable KDB's value to the team is much higher because of his global impact on matches.
So £60m-£65m is fair price for Mahrez. Barca overpaid for Coutinho but really who were they going to get to replace Iniesta? Liverpool overpaid for VVD in the same way we "overpaid" for Ederson.