Against weak sides that we'd pretty much beat no matter what - yes.
Against strong opposition where our defensive midfielder must not only win the ball but must function as an incisive passer even when under pressure - Fernando doesn't cut the bill at all.
It's a huge drop off in performance - even more I'd say than replacing Bravo with Caballero.
Fernandinho is our most irreplaceable player IMO, closely followed by Bravo.
Of course if Fernandinho could be replaced like for like then it would be done. But I haven't seen anyone so far, to do that, either in our squad, nor anyone else's. He is the best imo.
Gundogan imo, is a great player (when fit) one of the best, but he's not Fernandinho & can't replace him in that job, unless the rest of the team is also changed to balance it.
Fernando is great defensively but not Fernandinho in other areas.
We need to remember however, that Fernando has been playing under The Pelle . We have never seen him fully fit, with a run of games, in a balanced team. He turned in one or two top quality performances when Pelle changed tactics briefly.
We have seen Fernando in a midfield two, sometimes with Yaya, in front of Demichelis, Mangala & last season's Kolarov. We started that team v LIVERPOOL. Gundogan in the same position, under the same manager, would have had the worst game he has ever had, since he first kicked a football, even if 100% fit.
For all we know, Fernando behind Gundogan & A.N. Other with wingers & fullbacks dropping in & pressing etc, might be a fantastic pairing.
Kolarov for example was no less vulnerable or better at fullback on Saturday than he was typically last season, but it got covered by the team.
We have not seen Fernando play a run of games under a competent manager, let alone working for Pep.