I'm ambivalent about the 3 CBs and wingback system.
At times - against teams that defend deep or are defending a lead - one or two of them look redundant. It's less of a problem if they are capable of bringing the ball out from the back and joining the midfield/attack or their long passing is good enough. But, really, only Romero falls into that category.
At times it also leaves our midfield duo overwhelmed. Particularly if the front three aren't pulling their weight.
However the wing back system gives us width that we wouldn't otherwise have. This creates space for Kulu and Son. I don't think it's any coincidence that Son's goal surge in the last 10 games has coincided with Sess's reintroduction. Sess may not have Reggie's raw pace - to the naked eye anyway - but the timing of his runs and positions are better. His movement creates space for Son.