@dawn16 If you follow the link for planks you'll see it's a progression and the higher levels are actually pretty difficult, so I wouldn't necessarily class it as a warmup move.
As far as the higher rep ranges I briefly mentioned in the post this idea that it's beneficial to have a variety of rep ranges. So the higher rep ranges meet that need.
Also, people definitely tend to overestimate the degree to which high intensity is superior for muscle growth. Brad Schoenfield even did a study demonstrating identical muscle growth in well trained subjects between the ones using an 8-12 rep range and those using a 25-35 rep range.
As far as the higher rep ranges I briefly mentioned in the post this idea that it's beneficial to have a variety of rep ranges. So the higher rep ranges meet that need.
Also, people definitely tend to overestimate the degree to which high intensity is superior for muscle growth. Brad Schoenfield even did a study demonstrating identical muscle growth in well trained subjects between the ones using an 8-12 rep range and those using a 25-35 rep range.