Where did you have your muscle biopsy done?
Do you know how expensive and painful these are? I don't care about the pain (I refuse local anesthesia), but paying $1k-$3k and needing some rest days afterwards is a serious investment when there are other ways to find out/guess it.
Magness in his great book "Science of Running" listed many methods to find out if you are more ST or FT for your event.
Get on the track with other people with the 10k PR (for me, ~35-35:30 min guys). Run a few 100s with full recovery. Some will be significantly faster/slower than others.
Look at races. Who can destroy the others (runners of similar ability in a distance race) during the last 100-200m? FT guys are struggling to hold on for the entire race but often have just enough left for a last, devastating kick at the end to win the race. Championship races are a great example for that. ST guys like Salazar, Ryan Hall, Ingebrigtsen, or Paula Radcliffe won't be able to win international championships in track races. They realize they need to run away from the field at one point. If they can't do that, they are toast.
Standing broad jump, single leg hop test, all are indicative of muscle fiber ratio.
Look at your own PR's from 400-10k and compare them with IAAF tables or Jack Daniels predictions. Are you stronger on the shorter races or on the longer ones?
Lactate testing. A ST monster might only be able to produce 8 mmol after an all-out 400 (which would also be slow, compared to his 5k/10k race performances). That's very low. A FT runner can probably reach 17+ mmol after a hard effort, and the 400 would be much faster.
I agree that it's not always black and white, and being underdeveloped aerobically also has big influence.