For COMPETITIVE runners, it's base work ("as long as possible"), followed by hills, then intervals, then sharpeners.
For recreational runners, yes, it's LSD, more so for injury prevention and sustaining the activity as well as avoiding burnout. Lydiard would make statements like "no one ever pulled a muscle jogging".
The 80's and 90's saw a shift from the Lydiard competitive model as "low miles" runners emerged (Jim Spivey, Seb Coe, Vicki Huber, Suzy Favor, etc.). Overall depth suffered and eventually the US and Great Britain declined as "distance powers". Short cuts like weight training, plyometrics, form drills, "core training", etc. as well as possible PED use reduced the amount of "marathon training" used.
In addition women were finally able to run something other than the 1500 or the marathon in the mid 80's. In the 70's and 80's it was not uncommon for women to train for a prize money marathon while also racing 800's and 1500's. With competitive 3000 then 5000 and 10k's, "marathon training" became obsolete.
With Ritz having done "marathon training" and popping a huge 5k PR, I think the pendulum is going to swing back to traditional Lydiard training with milers doing 16 to 20 mile long runs (like Walker, Scott and Ovett used to do) during their base phase.