Overlapping/traditional full-back mostly just make one-timer cross/quick 1-2 with winger and runs back into position. Also he provides width to our CBs and CMs during build-up in less crowded pitch areas. If we lose the ball (mostly its not fullback who loses it) then its easier for given full-back to track back and cover his side - because of his starting position.
I find it much less riskier than playing as some sort of 6 during build-up on our half, and as 10 when in possession in final 3rd - mostly because we expect our full backs to operate in very crowded areas, where its easier to lose the ball. And for guys like Udogie or even Spence its not natural environment. We lose ball in such scenario typically means whole wings are exposed.
Also worth to mention that with traditional fullbacks usually only one is involved in final 3rd at once, so another can sit deeper, or join at later stage of action when ball switches side. In our gameplan, we usually involve both of them at once.