I think there's a relationship to water-resistance and loft simply because of the heavier, less flexible fabric.
As for the Marmot Precip - you might have one of the older ones - I know I did. Great for wind, but leaks like a sieve in a good downpour. I think Marmot will replace the older ones - I intend to try that route. Last summer I had the older one - it's an anorak which I prefer - and was caught in a heavy shower on a hike to Balu Pass up in B.C. It leaked so badly the water accumulated at my elbows as I was using poles, and about every 10 minutes I'd have to straighten my arm and let about 1/2 cup of water drain out. I bought a new one, and have been assured Marmot fixed that problem.