What people seem to forget is that we played with Delph as LB that season. Fernandinho was great, but while we were in the final 3rd, Delph would invert and sit next to Fernendinho as another holding midfielder. There was less space in midfield for opponents to play through, but the space was over the top to our left. Also let us not forget that although we were defensively solid in the 17/18 season we escaped with a lot of last minute winners. Both games against Southampton, Huddersfield, West Ham to name a few. Some of those results could have easily been draws.
When we played with Mendy this past season he had to stay high and wide to provide width which was hugely different to what Delph did. Rodri had to shift over, but he had too much space to cover. That's why at times would play both Rodri and Gundogan, but it did make us more porous in the midfield when the ball was lost.
I'm hoping this season Aké will do what Delph did and sit next to Rodri. Aké has the pace and can defend better than Delph or Zinchenko against counters. However, this would mean the forward players would need to create more by themselves instead of having an attacking LB like Mendy. But I do think with possibly Torres on the LW and Phil or Bernardo in the middle we can create enough chances and still be better against counters.