You're already misunderstanding how /dev/random and /dev/urandom work today, or indeed ever worked. Both devices have always read from the output of a CSPRNG.

It used to be that /dev/random did some accounting to try to estimate how much entropy was in its pool, and if that number declined too low (as reading from /dev/random was figured to decrease the entropy), it would simply refuse to run its CSPRNG to produce any more output until it get fed some more entropy. This accounting was heavily criticized for being magic thinking and unsupported by any actual research, and revisions to the randomness engine in Linux over the past decade have eventually eliminated this entropy accounting in favor of just tracking how much has ever been added--if there's not enough, then it blocks until there is.