I think it is hard to compare HID to LED, and comparisons that are made, are vague at best. I never cared for LED = HID comparisons.
I think where Fero came up with 400w HID comparison, my test growers initial testings of that spectrum/ratio/intensity per watt per color, from 173w, we pulled 4-7oz per light from multiple strains. And the average grow from a 400w HID is 1/4-1/2LB, but it is also possible to get a full LB from a 400w HID. There is no way in hell this 173w light will ever pull a full LB. And I also believe the average grower will not be getting 7oz without a little practice first, and also high yielding genetics.