I've run the course and my athletes have competed there three times. It's a short walk from the two mile to the finish line and the finish is only a few feet lower.
Your 1500m drop analogy is rather extreme. My argument was that a flat last mile would be faster than the last mile at John Hunt. Yes, you have a long gentle downhill a little after two miles, but the short climb negates that.
I manage several large meets a year and while our home course is accurately measured, it's a much faster course than it looks because we mow the grass very low and the footing is very good. John Hunt has longer straightaways, less hills, better grass and better footing than our course. I'm not surprised it's lightning fast.
You're always getting into arguments on this site, so I'd love to hear your background.