1) Energy budget is not that infinite, and light sabre is no a realistic weapon and in general melee is a bad idea. The only reason why Captain crunch is good because it is more an assist unit with mobile factory on the rear and it reclaims everything in its way, some AA, and the way it attack makes sense, since its weapon is a shredder which is extremely tought and so is its front armor, and with it fast forward speed it can be really good a fighting in "corridors" or to push a bunker position
2)They don't need a fusion reactor for home, they can get infinite energy from the Sanctuary itself, it is a giant solar panel, this is the reason why lore lords want second resource to be plasma and not energy, it doesn't make sense that you can be love on energy when you are fighting on biggest power plant built by humanity. And their vehicles? Why not, it is very effective, ecological and doesn't need to be refueled often