Of course, but in my experience you rarely, if ever, spend the entire cruise in cloud with limited visibility.
To artificially subject yourself to zero visibility is a bit daft.
Would you agree that the longer you spend not being able to see outside the chances of you twonking something are increased?
You can rely on TCAS and Radar all you like, they aren't infallible or 100% reliable. Uberlingen springs to mind.
What would you do if you were in the cruise and you had an RA out of the blue (which does happen)? Follow the TCAS commands and attempt to locate the other aircraft visually. You can't do both if you've got charts all over the place.