Whatever he may used to be, Fernandinho was a brilliant DM for City till last season. One of the best in the world, he was definitely world class in that position. If you think he was average defensively, perhaps you haven't watched enough of City. This season, even Rodri hasn't been able to replace Fernandinho adequately and that has been one of City's problems. Fernandinho now plays as Centre Back, though at 35 he hasn't been able to perform that role well. But he has done better as a CB than Otamendi or Stones. At 35 as a CB. Not good defensively? You gotta be kidding.
A midfield 3 of Eriksen + James + Barella/Brozovic is shite IMO, even though individually I rate all these midfielders highly. That midfield will get clobbered off the ball. No coach can make that work. Balance in a team is important, this is not fantasy football.