My impression of DJI isn't so negative. Analyzing a lot of flights I sometimes get to know the final disposition. Usually, DJI is better than this. I think that it depends on who you talk to a DJI. If I were you I'd keep at them. Try to talk to someone different, i.e. go around the person you were talking to. It should be easy to get to a point where it's clear it wasn't wind and was the gpsHealth issue I described.
The problem that you'll have is that a low gpsHealth could be due to factors unrelated to the P3 hardware. I'd argue that the fact it abruptly dropped to 0 and then never recovered makes it more likely the problem was on the P3.