Paragraphs my friend,
I have a score of 460k without downing and probably having all challenged complete. Maybe downing affects your overall score then.
A lot of people who had 500k probably had a support team helping them out who would protect them and let them get most of the kills.
Stinky666 helped me get both of my high scores on Point of Contact.
Congrats on doing it. I guess 5 relics solo was pretty hard and it must have taken a lot of effort for you to do it.
I'm currently working with some others do to a 4 player 5 relic run. I don't think it will be too hard with 4 players though. Point of Contact is easy enough only having 2 people run 5 relics on it.