I can only attest to this.
I trained competetively 2000-2004. And in my teens (13-15) I trained periodically (1995-97).
We didnt know HOW to train. Every run was more or less a race or became racing at some point.
The coaches put everyone thru the exact training regime. There was really no understanding how each person responds differently to training.
There was an aversion to high mileage (especially in the 90s) and we seldome aimed to reach a certain mileage or tracked the miles run (early 2000s). It was not a case of "I need to run a certain milage". (I prolly ran about 45 to 90 km per week during those years 2000-2004). It was "go fast n hard or go home", "train hard, win easy".
I switched coaches after about 1,5 years (around 2002) and the training I started with the 2nd coach was much harder than I had done before. I remember I was suffering in the beginning. With my first coach I used o run sessions of say 6 x 1 km (ca 1 min rest) at around 3:15-3:30 min per km. We were a small group (maybe 3-7 runners), about the same age (early 20s) and it was more laid back and sometimes, if I had been injured or ill I used to run with the girls which meant paces of even slower, maybe ca 3:40 min per km.
With my new training regime I was in a big group of highly competetive male adults, many of them national (or in a couple of cases even international) elite. Each interval session was crushing. I used to do 5x1 km (ca 2 min rest) at around 3 min per km. But the best guys was prolly doing them at 2:45-2:50 min per km. It was killing.
Not to mention the WEEKLY hard interval session on track with spikes. A pyramid session 600-500-400-300-200 all out with 5 min rest in between was a recurring theme. Totally insane in hindsight and with todays knowledge.
Yet I ran more or less the same race times. I remember observing this fact (training harder but racing not improving) BUT unfortunately I didnt reflect and react or to it.
With todays knowledge I can def say I flourished while doing more threshold inspired work around 3.30 min/km while I suffered (broke down) while trying to compete in training with others n running around 3 min per km which def was above my threshold level at that time.
It took me a couple of years to adapt to the new traing regime and then, when I was finally flying, I got injured which eventually ended my running career.
In hindsight I should have run more and less intense. Slow, easy distance running, regularly twice a day and with 2-3 threshold sessions per week. That is, the Ingebrigtsen base training would have fitted me great, but Im not sure how they train during race season or the weeks leading up to race season...