Where/what are your anchor points?
Like yours, mine are simply screwed into the decking but...the decking is 7/8" plywood, not OSB. You might have mis-understood where the failure occured. It wasn't the E-Track anchor that failed, it was the ballistic nylon strap between the E-Track locking device and the "D" ring which my tie-down strap attaches to.
I think that one of the things that contributed to the failure was that this particular tie-down was for the rear of the bike. When I load and strap the bike it DOES have a constant load on this strap, but as we go down the road the strap can work itself into a different position and slacken just a bit. This would put a "sawing" type movement on the tie-down and if the road is rough might lead to failure.
Basically, you need to keep in mind that although quality tie-down straps are expensive, they don't last forever. I tend to replace my primary straps about every two years. When those get replaced I usually put the old primary straps into the secondary position.
Just for info purposes: Most of our hauling is carting around our 2006 Yamaha Stratoliner (about 800 lbs.). We have used the rig to transport our Rhino though with a weight of 1,360 pounds, it puts us too close to GVWR if not over by a couple hundred pounds.