Not a direct answer to your question, but interesting to note that the online ME workout that is very similar to the ME workout in the Big Vert plan has core work as part of the warmup: https://uphillathlete.com/at-home-muscular-endurance-workout-with-progression/
Might be that the online version with core workout warmup is more generic and the one in the Big Vert plan with the running warmup is more running specific?
Personally I do either warmup before ME depending on my mood. 🙂