Fullbacks sitting deeper is fine as long as the wingers stay high and wide and make runs in behind (see man city and Bayern and Juve). Son and Lucas however, are allergic to playing out wide, they're more like second strikers than out and out wingers. We also give up so much creativity by playing winks and Sissoko, who then don't do enough defensively to compensate for that. a) How often do those two pass the ball sideways to each other or a defender, or b) receive a pass and then turn their man and get goal side of him before playing a threatening pass? I'd say a) almost always, and b) almost never. Here's what I want to see from us.
Lloris
Back 4 (who gives a shit about this lot as long as Toby and Jan are in the middle)
Ndombele Dier Eriksen/lo Celso;
Lucas (sitting out on the right touchline, up on the defensive line) Kane Son (sitting out on the left touchline, up on the defensive line)
Defensive nous in the middle provided by dier, creativity and quick ball movement in the middle from Ndombele and Eriksen/lo Celso.
Width and pace mainly provided by Lucas and son, who should almost always be attempting to get goal side of their respective fullbacks via diagonal runs once Eriksen and Ndombele pick the ball up in the middle. Ultimately these passes should be going in between the CB and FB. In this system the fullbacks don't matter as much in terms of offensive output, they can sit in and halt counters and provide an option for the pass from the CB/winger/midfielders in a triangle formation to progress the ball quickly. The centrebacks shouldnt be too far apart, however the fullbacks don't tend to play close to them