Respectable people believe quite strongly that DCR is important, but I'm convinced that it's superstition.

The basic idea is that intake charge flows back out the intake port while the piston is going up in the cylinder. Which is true at idle. Maybe even in cruise.

But if that was true at full throttle and/or high RPM, closing the intake valve later would give you less power at high RPM. But generally speaking (e.g. excluding pathological scenarios) delaying IVC give you more power at high RPM, because air continue to flow into the cylinder until the intake valve closes.

At high RPM, air is not being pushed out of the cylinder while the piston is rising.

And that tells you that DCR only matters when airflow is low - conditions like idle and cruise. Air behaves the opposite way when we're making power. DCR is red herring.