I won't say you guys are wrong and I certainly had some background, I didn't run a sub 15 5k from nowhere and I am happy to discuss with you as you seem to understand a lot about training.
The funny thing is that when i started increasing my mileage (I was running an average of 55 mpw before) my times for longer distances got worse. I did improve my 5k in 8s, but that was a result of a huge effort in a race that i nearly died after crossing the finish line. I was actually disappointed.
I had a 32:06 10k PR and of course as I was expecting to break 32:00 easily as I was expecting to break 15:00 for the 5k. To be honest i was hoping I could run under 31:00. "Well, if I am in 14:50 5k shape, than I am certainly in 30:50 10k shape)
One month before my 5k race (when I was running consistent 90 mpw with peaks of over 100) I've raced a 10k and finished in 32:10. I thought that maybe it was because I had started a little faster than I should, as my first 5k went through in 15:35 (I was hoping to run a 15:25 second 5k and break 31:00). The 5k race proved I was wrong, and running 15:35 was so close to my max 5k performance that i died in the second half of the race.
The half marathon was worse. I was told that I was at least in 69:00 shape. My PB was 71:30 so i was expecting to cut more than 2 minutes. After running the first 5k in 16:20 and the 10k in 33:00 I started dying and finished in 72:30. My second 10k was close to 36:00 and I was jogging for the last mile with no fuel at all.
If I'd run even paces, I could have probably run a 31:50 10k and a 71:00 half marathon. But it was not a great improvement after all I had trained.
The 5k in 15:19 was really the best that I could have done. My laps went consistently in 73-74 and I nearly died in the end.
Maybe you are right to the point that I moved to fast to 100 mpw. But well, i spent years running 60 and then progressively went to 100. It was like 65-70 the first two months, and as I had years of running 60 it really didn't make a big difference. So got up to 75-80 and stood that for more months until I felt comfortable. i was obsessed with the 100 mpw number. I used to read articles, lets run posts and everything else that emphasized the fact that i should be running 100 mpw to become faster.
After six months running close to 100 mpw and disappointed with my results, I thought it was not the training the problem, but myself.
Did the 100 mpw help me to build great aerobic conditions? Maybe. I think I already had when running 60 mpw. Remember I've run a 15:27 5k and a 32:06 10k. Could I have run faster than that keeping my mileage? I think I could. Also, I did stop training for almost one year. barely jogging three times a week. My aerobic conditions should have eroded already. Maybe i will never break 15 5k again and will start running 15:30 again as someone suggested.
I suspect that I can still get faster running no more than 50mpw.