Jim Beam running formula
Weight training and stretching for runners has been prevalent since at least the 80’s. Go look at Coe’s training - heavy squats and tons of core. While helpful, they are not the key differentiator.
Look at mid distance times, which theoretically benefit more from the training noted above. HS 800 record is from the mid 90’s. Mile record from the early 00’s. 3200 relay times have not improved materially.
Biggest differentiator in current training, as evidenced by performances at 2 miles and above, is increased focus on aerobic and threshold training. Current coaches and athletes are universally better educated in that regard. No more hammering intervals 3-4x per week and neglecting base mileage and threshold work.