Hi Les,
Welcome to the world of resin! Yes, it can be long lasting although some resins (mainly epoxies) can cure softer than glass. I haven’t ever weighed equal amounts of resin castings and glass cabochons, but in my experience, yes, resin is lighter. Resin works well to fill bezels, but you have to worry about bubbles there too. The good news is that if you are careful in mixing, that will minimize the amount of bubbles you have.
I haven’t used Amazing Glaze, but I think resin produces a thicker, higher dome as compared to Diamond Glaze.
Does this help?