This is my understanding as well, the VDP is the optimal point at which
to start the descent to the runway if 1. the visibility requirements are
met, 2. the aircraft is continously in a position where it can land
using normal maneuvering and descent rates, and 3. has the runway
environment in sight.

The longer you fly after passing the VDP, the harder it becomes to make
the landing. This does not mean that you're not ALLOWED to descend prior
to the VDP, and in fact you very well may be if for example the VDP is
identified through a dme distance, and the plane doesn't have a dme
onboard. In that case, you level off at the MDA and upon establishing
visual contact with the runway, you descend as you deem appropriate and
land. This MAY result in you descending below the MDA prior to the VDP,
but you wouldn't know it. If the approach is designed correctly then the
point where it feels natural to start the descent to the runway should
more or less coincide with the VDP anyway so it shouldn't be that big of
a problem.