There is vertical guidance (VNAV) for VOR and NDB, and yes you can cross reference DME/ALT scale. However, how valid is a check 0.25 nm prior to the runway when a DME is rated +/- 2nm? The problem is on a GNSS approach you have no other reference to cross check.
Cross checks cease have much meaning that close to the runway, in reality once you are below the minima you are almost entirely dependant upon the visual picture to judge where you are relative to the runway, monitoring ROD & speed. In fluctuating visibility and passing showers resulting in a loss of vis close to the runway you are in no man's land. The only safe option is a missed approach.
The difficult one is the last couple of hundred feet in rain as the forward visibility deteriorates temporarily with the changes is rainfall intensity, the picture keeps coming and going as you pass in and out of the shower. I would not take long to get 140' low if the sink rate goes to a 1000~1200 fpm as you are continuously changing focus from inside to outside. It's only a bee's d!ck change in attitude or thrust to go from being right where you want to be to be low. A sudden reduction in the visual picture at just the wrong time can end up like this accident quickly.
There was no mention of who was the PF,.
I did note the FO only had 368 hours on type.
Were the runway lights on? The
Airport info page also makes the remark " Marking: precision, in fair condition". I wonder what it would have looked like under overcast and rainy conditions, quite grey, and similar to the water, making visual perception relative to the more difficult.
You are also dependant upon the support pilot to call deviations in ROD or speed.
You can see in the image the FO's windscreen wiper is stuck half way across the window, so it was likely on at the time of impact. Captains side not visible out of stowed position, however, without looking at the switch position, you can't conclusively say if it was on or off. But the fact the FO's was on indicates they had probably experienced rainfall during the later stages of the approach.
Lots and lots and lots of ways that this type of approach can go wrong. Lots of questions.