Since I don't have my rings yet I am just guessing here.
I think you have a valid point on the "bunching" of the webbing. More of the fibers bear the load if it is nice and flat, instead of bunched up like a knot. Okay, that makes sense to me now I think.
But it slips and you still gotta use a knot, even though the knot doesn't hold the lions share of the load. I guess if it slipped enough it would, then your back to relying on the knot, mostly anyway.
I have never seen a knot breaking strength comparison chart for webbing, just rope. And IIRC the slip knot wasn't one of the knots tested, but I will need to find the link to know for sure, I think it was eight knots.
However, using 1000 lb breaking strength webbing, with, a bowline in it (70% breaking strength I think) we still have around 700 lb SWL, of course this is for rope not webbing, but like I said, I lack the data.
So all things considered, to me, a knot is simpler and lighter, but not as quick. Even tho the braking strength "may" be lower than the buckle system, it is still within my weight limits; I haven't had a failure yet and I have been using knots all along.
Geez, how hard can it be to suspend a friggin' hammock? I should've had those rings shipped priority instead of standard...