Gamma/Energy guns are woefully underpowered in this game that most people don't bother with them.
Under 30 dmg at lvl50 doesn't sound like a 3* legendary.
The TSE's are very valuable, I've seen a double with about 1100 damage, and a pump action with about 800 damage. Those would take down a scorchbeast in a couple of hits.
With my perks and mods, my ordinary combat shotgun does 200 per shot and has a very high rate of fire for a shotgun. That's a lot and it minces things quite effectively. I can solo 3 scorchbeasts and a pack of scorched quite easily, with the only significant problem being the screaming effects making it hard to see where to shoot. 800 on a pump action would be a bit mental. What does TSE stand for? I'm assuming that the E is Explosive as I know from my weapons in FO4 that the explosive effect is huge on shotguns as it applies to each pellet.