I'm a little disappointed with mine too. I just moved a plant out from my 275 watt LED lit tent, to my big grow space to get the HPS on it. I like my 1000W dimmable ballast a lot. It's running in a cool tube with a hood. I've only ever run HPS bulbs, but I think I'll try a veg run with the MH bulb, just because I have it.
What I got out of the LED last summer is pictured below...I think 5-6 Oz maybe. I'm not big on weight measurements, but half a gram per watt for LED seems to be the average and I got that. What sort of yield are you getting from your LEDs?