I think you're off by an extra zero on your front axle numbers. Not even commercial trucks run that high a weight on their front axles. Well maybe one of those 3-4 story haul trucks in a mine perhaps.
As I see your numbers you overlooked the 100 lbs that transferred to your front axle when you weighed without the trailer. With the trailer your truck weight totaled 7280#. Without it weighed 6630#. This gives you a tongue weight of only 650#.
Weighing only one axle at a time is perfectly OK. It's merely showing the weight of each axle as it sits on the road and nothing is really changing as you move from one to another. Only difference is you have to do some addition you wouldn't do if you weighed all at once.
Only thing that might change the numbers slightly is if the scale pad was higher or lower than the areas the remaining tires sat but scales like this are built with flat surfaces in front of and behind the weight pad to eliminate this issue.
From the above your trailer weighs 6130# and your tongue weight of 650# is 10.6%. Perhaps a little light but did you have your water tank filled?
I'm guessing not as the rest of the numbers seem to match my trailer and truck pretty close but when I weigh with the water tank filled the tongue weight is about 200# more. I also have about 100# of "gear" loaded in my front compartments and pass-through storage which contributes to that weight. The factory says my tongue weight is only around 580 something but that's empty.
Your numbers are not pointless and are perhaps more accurate than on scales where the weighing section is larger and you have to get individual axle weights by driving only part way on and part way off then doing even more adding and subtracting. This way each axle is being weighed with the same part of the scale.