You're ignoring the fact that the attacking players need to be supplied with the ball to enable them to do their thing. Yaya has the capability to play eye of the needle type passes through midfield that break the lines and find our creative players in the pockets, Fernando struggles at this.
Imo the 'eye of the needle' passes are exactly what we don't want to be attempting too much of when we are 2-0 up, & are often part of the problem because they give away the ball more than they open up the oppo. At the other end of the scale, people such as Clichy, Kolarov, Stones, randomly hoofing or heading the ball back into centre midfield or up in the air, rather than clearing it properly, is another huge danger. Simple, ball retention is what we need, then the oppo will provide the gap themselves, by getting tired chasing.
Fernando can do that, if needed.
But imo, the problem isn't whether Fernando plays or doesn't play, it's how the whole team operates together.
If they develop the ability to keep the ball, as a method of closing games out, like v Bournemouth, & Silva/KDB put in the hard work centrally, then there is not so much need for Fernando, other than to cover for injuries. But if it's 1-0 rather than 2-0, & we are playing a top 4 side, can we keep our nerve, & do it ?
Also, whatever formation we play & no matter how well we are playing, there will be situations where we lose the ball.
On many occasions this season, that has resulted in the oppo, with the most basic of moves, completely dumbfounding our back 4, as if Messi had conjured up something magical, when actually they just lumped it, or played it wide, like Chelsea, Everton, Spurs, Leicester etc did. Most of he goals we concede, are stoppable with competent, rather than excellent defending.
Where we need players like Fernando, Delph etc, isn't when everyone is getting it right, it's when they get it wrong & somebody has to win the ball back. We have had many of those situations & arguably needed two or three Fernandos to protect the back 4.
