Let's say you have a mediocre (2:00-2:10) 800 runner in their late teens with not so great speed. They currently have a decent endurance background, but seriously lack speed. If they started training at paces that would be suited for a much higher level runner, just broken up into small segments, could they over time reach the times that would align with their training paces? Assume they have the patience to incrementally work towards their goal over the course of years of work.
Example: Sub 1:50 training paces might be 6:00/ mile for easy runs, 4:45 for tempos, 4:15 for VO2 Max, and 3:40 for 800 race pace work. If a theoretical runner started training at these paces in segments with long recoveries, lengthening segments and shortening recoveries, along with weights, drills, and weekly sessions for basic speed development, could they achieve this? In this hypothetical, there would potentially be no "slow" running, potentially using low impact cardio XT until the volume of aerobic work at the specific paces given built up to reasonable levels for cardiovascular and lung capacity.
"Easy runs" may start out as 1k-2k reps at faster than 6:00/mile, tempos as 400 meter reps in 71, VO2 as 200s in 31-32 with good recovery, and pace work in 50-100m stretches at 3:40 pace with good recovery.