Descent rate, ie: "which reaches the ground first" is a factor of time, not angle. It's true, gliders don't carry water ballast for nothing, but for reasons you apparently don't understand at all.

eg: Assuming two gliders (eg: Discus b) with the same L/D (hypothetical nil W/V) one (full tanks) and the other none are both flown at respective speeds for best L/D. Does one reach the ground first? The answer to that is yes. See if you can explain which and why. Assume both are flown at Vmin sink. Does one still reach the ground first? Answer and why?

Quite apart from the absurdity of your suggestion of a light plane (ie: general case, not being eg: WWII mil dive bomber with speed brakes extended) being able to dive vertically without exceeding Vne, no parameters were given suggesting the case of a light plane or otherwise, which incidentally is immaterial. Certain assumptions must be made. Assuming you were trying to descend at as high a rate as possible, the limiting factor before the nose got too pointy toward ground would be speed and the limiting speed (structural) a professional pilot would fly at would be Vne.

Edit: sp