Mahrez has great personal talent no doubt, but his value to the team this season has been minimal.
I understand why people think he is lacking desire to play for us, but i don't think his work rate has changed that much from last season, there were many times we were getting frustrated with him last season, and several games he was a passenger.
There are many players with great talent who make average (or worse) footballers based on their contribution to the team. Tarabt comes to mind. It is also important to consider that many players through history have been able to produce 1 great season in a mediocre career (Michael Ricketts anyone?)
I think that whether Mahrez is a great player who has had 1 bad season, or an average player that has had 1 great season is a question that still needs to be answered for me.