The issue is that some level 10 characters could kill thousands of level 5 or less characters up to the point they could just solo an army of level 5 and less people.
In dnd 3.5 levels grants growing advantages: even the cr system assumes that 2 more levels means you can fight twice as many opponents of a given level and in practice it can be even worse than that.
So it makes sense in a non dnd world to have the most skilled people sabotage things but in a dnd world the most skilled people can facetank the opponent army and melt through it thus making any infrastructure it had irrelevant and it is arguably a more useful use because it means that your army will take less losses while the opponent army is busy being annihilated in a single day.