Visual separation at night in dense airspace has no checks and no margin for error. There is no way for anyone to tell whether the crew is tracking the correct aircraft or whether they are correctly guessing its attitude etc.
That practice is plainly asking for an accident to happen.
In the UK I know traffic is indicated with a relative position and altitude: “traffic at your 10 o’clock, 2 miles, altitude 1500 feet”.
The ATC for the Reagan crash did not indicate a relative or absolute position, only referencing “the CRJ”, which might be hard to identify in the dark, and the helicopter pilot may have assumed he “had visual”, but was looking at a different aircraft.
That practice is plainly asking for an accident to happen.