I take it that you're a distance guy and you don't have any sprint coaching certifications, because you don't seem to understand Hart's program. Clyde Hart's program is tempo based. The knock on the program in some quarters is not that there's too much intensity, but that there's too little for people with mediocre pure sprint speed before it starts.
If you go to one of Clyde's coaching seminars, just about the first things he says is that "You are not allowed to run faster than the listed times." The times given are for a 46 second university runner. So when you see a workout like
4X300 speed 40 sec
This is intensive tempo around 85% for a 46 second guy. Some of Clyde's training might seem speed endurance to distance runners because they can't run very fast, but I assure you that 10X200 in 30 sec is not speed endurance to a 46 second guy who can run a single 200 in under 22. That's more like jogging to a sprinter.
Yopu can find Clyde Hart's present 400m plan here:
http://www.ustfccca.org/assets/symposiums/2013/Hart_s%20Sample%20Workouts.pdf
Most 400m plans work more or less like this (ends to the middle). This is what you start with:
3 X 500-600 (75%) rest 10-15 min
3 X 300 (85-90%) rest 4-10 miin
5X 80-150 (fast)
This is about what you end with:
3X450 (90%)
320 (95-100%) 3X200 (90%)
3X200 (fast er than 400m pace)
There are no cookie cutter plans and no my way or the highway. You have to be able to adjust things according what kind of athletes you have and how they are adapting