Revisiting this concept, I think a great way to create this kind of set-up is just to establish what the consequences are if the faction doesn't exist. Doing so for evil is pretty easy; doing so for good risks falling into cliche (oh no, order is getting too orderly again!).
I think a good consequence for "Good" being too dominant is that people can really only remember their lifetimes and maybe a generation or two back. In other words, past threats get forgotten. It's not that peaceful times make for weak people, it's that peaceful times make it easy to forget what is necessary to maintain peace: strength, wisdom, vigiliance.
Such a situation may not sound too bad, at worst it may be cyclical, but that changes when you think about the scope D&D acts on. If Good gets caught slackin', then there's potential for things like extinction events -- dark gods ending the world, blobs of annihilation, great wyrms destroying civilizations, etc. So total might the destruction be that recovery will never be possible.
To that end, the neutral faction may try to create controlled scenarios in which evil is empowered so as to challenge good, and then switching to helping good overcome that evil. It is a very manipulative and morally grey set-up, and I'm sure you could make valid arguments for this status quo vs this status quo not existing. But this, IMO, is what I think is a great way to go about creating this situation of Muscular Neutrality.
The heroes finally kill the lich, only to realize that the lich was created for them to kill. Does that make the creators of the lich just as bad? Maybe worse? But now the heroes are strong, and they inspired their people, and now new heroes inspired by them will train and go out into the world. So there is a potentially a netgood. This works especially well if you have a character that is a Prophet/Diviner/Oracle in the muscular neutrality side.
I think a good consequence for "Good" being too dominant is that people can really only remember their lifetimes and maybe a generation or two back. In other words, past threats get forgotten. It's not that peaceful times make for weak people, it's that peaceful times make it easy to forget what is necessary to maintain peace: strength, wisdom, vigiliance.
Such a situation may not sound too bad, at worst it may be cyclical, but that changes when you think about the scope D&D acts on. If Good gets caught slackin', then there's potential for things like extinction events -- dark gods ending the world, blobs of annihilation, great wyrms destroying civilizations, etc. So total might the destruction be that recovery will never be possible.
To that end, the neutral faction may try to create controlled scenarios in which evil is empowered so as to challenge good, and then switching to helping good overcome that evil. It is a very manipulative and morally grey set-up, and I'm sure you could make valid arguments for this status quo vs this status quo not existing. But this, IMO, is what I think is a great way to go about creating this situation of Muscular Neutrality.
The heroes finally kill the lich, only to realize that the lich was created for them to kill. Does that make the creators of the lich just as bad? Maybe worse? But now the heroes are strong, and they inspired their people, and now new heroes inspired by them will train and go out into the world. So there is a potentially a netgood. This works especially well if you have a character that is a Prophet/Diviner/Oracle in the muscular neutrality side.