It's not a case of singling these players out. I think pretty much everyone accepts that Sawyers has been a huge disappointment, Simpson was a dreadful signing and Ojo is extremely frustrating.
However, you have a look at the team as a whole when attempting to assess why things have gone so badly wrong this season and, in my opinion at least, several of the side's mainstays just aren't very good by this division's standards.
City have played 30 league games this season. The players leading the appearances chart are:
Ryan Allsop - 30 appearances
Ryan Wintle - 29 appearances
Perry Ng - 28 appearances
Cedric Kipre - 27 (+1) appearances
Callum O'Dowda - 26 (+1) appearances
Of those five, I'd argue that only Kipre and O'Dowda are decent Championship players. They would get into plenty of other sides in this division, but how many other teams at this level would covet the likes of Allsop, Wintle or Ng? I know there are some contributors who rate these players for various reasons, but in my view they are well below average by Championship standards. They look distinctly limited to me. Meanwhile, I think most of us agree that Ralls is having his poorest season since arriving at the club.
Saying that doesn't mean the likes of Sawyers, Simpson and Ojo get a free pass by any means, but stating they haven't been good enough is like saying today is Sunday.