It's not even inverted full backs these days. For a lot of the last two seasons, it's basically been four centre backs, with Walker not inverting (because he's shit at it) and not really going forward either, and Ake doing the same on the other side. Gvardiol has got forward a bit more, but he's still essentially a CB and doesn't really have a cross on him. One of the basic tenets of having inverting wingers is you have someone to go on the outside of them. That's why Grealish and Bernardo linked up so well on the left at times.