You are technically correct about weight, however, my compression sacks are sil-nylon, and are significantly smaller than the original tent bag. The additional weight penalty is less than an ounce, which I'll easily accept. The gain in volume reduction with a packed tent and rainfly is significant. The tent bag is 60% larger than the compression sack, and that is even before it is compressed. The compression sack is 8.4L and the tent bag is 21.3L. The trick is to stuff it, not roll or fold the tent.

My 45 degree sleeping bag compress down to the height of a water bottle. I also use compression sacks for my puff jacket. It works for me