Inverted fullback isn't that bad if player does his chores well.
We have won PL with Delph and Zinchenko for many times.
Cancelo also, wasn't he something like that ?
But what Rico lacks is efficiency with the ball, there is no excuse in loosing ball as much as he did yesterday, cause if we aren't solid in our buildup and possession and loose the ball easily there, then our whole system cracks.
We have a luxury to loose balls in the final third, because that's where our defenders and midfielders are able to intercept it or take a foul if needed.
But when you loose it in our third or midfield third, then it's obvious that we are exposed and opponents can hurt us.
It's like.. if it wasn't John stones in treble season and we played Ruben in that role, most probably we would suffer a lot, but John was playing very efficiently and helping us, never hurting our possession and stably / efficiently delivering it to the teammates.
So it depends on the player.