I think some matches (either to start or as a strategic option for late in the game), having a 4-4-2 formation makes sense. Sigurdsson would need to either (i) come off the pitch; (ii) move to a LW or DM role (I am pretty sure this works best with Iwobi and Richarlison on the wing, but maybe not every time); or (iii) possibly as one of the "2" if you want to see how he operates playing off Kean.
But the point of a "no Siggy" formation is that you'd use DCL playing off Kean to open up space for Kean and Richarlison (and to a lesser extent, Iwobi) to create goal scoring opportunities.
Let's say Siggy doesn't fit this at all (may or may not be true) - I still think you only run this 20-25% of the time. It's not like he gathers cobwebs.