Yes, I'm not really familiar with Gundam, BattleTech and their like, but don't they need really small and efficient fusion reactors? We're not getting those anytime soon unless the technological Singularity AIs design and build them, but we'd likely have things other than giant freaking robots to worry about then.
But within the Trek Universe, "
MicroFusion Reactors" can scale from personal Generator size that is man portable to powering DS9 if need be.
Don't forget ultra compact energy dense battery sources.
So Energy isn't a problem at that level of tech.
The big issue is that the more dangerous/powerful Energy Reactors like M/A-M, AQS (Artificial Quantum Singularity), Tetryon Reactors, & ProtoStar Containment Reactors are for more dangerous when used on the surface of a Planet.
The failure mode for those would be VERY bad compared to a Fusion Reactor.
M/A-M would be even deadlier than a Fusion Bomb.
AQS could become a run-away artificial Black-Hole if placed on the surface of a Planet.
Tetryon Reactors could release too many Tetyrons into normal space that could react with normal matter causing untold destruction.
Having a Baby Sun on the Surface of a Planet would be a recipe for disaster.
No matter how I look at it, all those more "Advanced Energy Reactors" are better off in space on a StarShip or StarBase.
Fusion & Fission are far more "Safe" when Planet-Side.
And those are just "Relative Safety" factors when they fail.