Exactly this.As stated this is not about whether or not Mahrez is a good player, he is clearly a good player.
The point being made is that this team doesn’t have the full backs to accommodate inverted wingers and because of that, we look a much worse team now, than we did 2 years ago when we played with traditional wide men. Opposition teams typically pack the middle against us, they know our wingers want to come inside and our full backs can’t/won’t overlap and hurt them on the outside. If Mahrez had TAA (or similar) behind him, I would have a completely different opinion on this.
For me, we either go back to wingers on their correct side, or we replace Walker with someone who can step foot into the opposition half. There was little wrong with the Sterling/Walker partnership on that side, whereas Walker and Mahrez are an awful double act.
Without a fullback to overlap, Mahrez is kind of forced wide quite permanently and far from goal.
His main assets are goals and assists and close ball control/dribbling, at Leicester he always had a fullback wide right and could play inside, he even played as a 10 for Leicester for large amounts of time and was successful.
Now the counterpoint to this is that KdB sometimes goes wide (if KdB is playing RCM) to let Mahrez come inside, but this doesn't happen nearly enough (KdB barely played the last game and didn't play well, that's okay) as a fullback does for their winger.
False 9 Mahrez should be seriously looked at (or atleast play him as a 10), Sterling right and Jesus left (I've liked him as a winger). He is quicker than Bernardo at it and is quite good at scoring with both of of his feet. I use to think Bernardo was the closest thing we had to a false 9 Messi, but now I think Mahrez (or Foden) are better.