In case of block training, periodization, and other non-traditional training methods, how can they be compared to traditional which is more trained?

If traditional is more trained there is less gains to be made in that training method. If this is compared to "new" methods, the gain in those methods will be higher because of being less trained.

So how can this be properly compared? Of course with new trainees this can be done, but what about expert athletes?

Endurance training

HIT

Long duration versus short duration.

High intensit Interval training.

Interval training