I personally find this to be one of the major plot holes on dragon ball which makes any intention on defining their real powers pretty hopeless, although if there's something that explains it, which I'm not aware of, then it's not a plot hole.
I mean, depending on the situation if their ki based attacks hit something the effect can greatly change according to the situation, it can destroy just some landscape, a huge amount of it, a planet, a solar system, a galaxy...
If their energy attacks just destroy some landscape then there's no point in using them against enemies that could stand to something that would destroy a galaxy, so there's no reason for them to be used and it would be pointless. If they cannot control their destruction output everytime that there's a fight with their current power level the whole universe would be destroyed if some amount of ki based attacks are used in the fight and don't exactly go directly to one of the fighters.
But maybe they can control it according to their will of how much destruction they want them to cause.
Is there something that explains that seemingly relative destructiveness of their ki based attacks?