No experience with MB's clothing.
If you're talking about the UL Spiral Down Hugger sleeping bags (or super stretch), there has been some discussion on under-filled bags. However, from what I hear, that was a year or two ago, and there really haven't been too many recent complaints to my knowledge.
One thing with their sleeping bags is their "stretch" system works differently than traditional bags. Even though the down may seem thin in some spots, the stretch bags are supposed to pull the inner fabric closer to you while allowing the outer shell to poof up and promote more loft.
This is my understanding of it, FWIW. I've got a MB Super Stretch 40 degree, and yes, there seems to be some thin spots in the insulation. However, I've had that bag down to 40 degrees many times without ever getting cold.
Loft and density of down is not always a consistent indicator of whether a bag will be warm or not. There are so many other factors!
Did you ever try the jacket and sleeping bag on backpacking trips or in your back yard at least? If you tried them and they didn't meet your expectations (or claimed performance), then they simply weren't for you; no arguing with that. But if you simply judged them by their *perceived* short-comings, you might want to at least give 'em a real try!