My 8x10 KB Canham weights 8.4 pounds.
The same camera at a 5x7 weights 6 pounds.
Not much difference at all. The joy of a bigger ground glass is why I love 8x10. It is not more cumbersome if you get the right camera for your needs.
Comparing 5x7 to 8x10 is a lot like comparing apples and oranges. Their aspect ratio do not match. I love shooting 5x7 for what it is, just as I enjoy 8x10. They are tools. No one format is perfect.