1. Yes, for many of the benefits of GLP-1s, it's plausible the mechanism is weight loss. But actually achieving significant weight loss with other therapies is incredibly hard, so I think GLP-1s get some credit here.

2. Hunger signalling isn't the only thing GLP-1s do, so no, we should not just assume every effect stems from weight loss alone. E.g. the blood sugar regulation that makes them very effective for diabetes is not purely about weight management.