It is difficult to defend flying ahead into a place which you cannot assure is clear of traffic. That said, most fixed wing aircraft I have flown, even twins, have an appallingly poor forward low range of vision for the pilot. If a pilot chose to do clearing turns to assure in front below was clear before a descent, they would have to be very large heading change turns to be effective. In cruising flight, this would result in considerable excursion from the intended course, and indeed introduce even more opportunity for conflict with aircraft "maneuvering" where they would be expected to be following a course. It's certainly an imperfect situation, 'always has been. Three times while established on final approach, and having broadcast my intentions, I've had an aircraft appear high and in front of me, descending into my path, as they did not see, nor apparently hear me. Once took a pretty aggressive dive to get away, and I was not all that high to begin with.
Helicopters certainly have a major visibility advantage over most types of fixed wing aircraft by design. The helicopter design criteria gives very specific and clearly defined angular dimensions for the required angle of view, accompanied by a drawing, in the Advisory Circular for certification. The fixed wing equivalent AC criteria is very brief, and subjective to the evaluator.