So the "Gray Jedi" thing kind of misunderstands the terminology of "light side" and "dark side" as it concerns the Force. Never mind that "light side" itself is a post-movie thing as there it was generally understood that the Force is, in itself, light (meaning good) so there wasn't any need to refer to it in those terms...
But the main point of confusion seems to come from viewing it like a brightness color meter where on one side you have pure white, on the other you have pure black, and in between there's gray. Hence the idea that you can just kind of balance the two and get all the benefits with none of the sacrifices.
In reality it's better to think of it in the dictionary terms. Wherein "dark" means "absence of light" meaning that there's some gray part in between. There's just light and if you don't have any of that... There's darkness instead. Nowhere in Lucas writings is the Force really described as this two-sided thing you can balance. You're either good or you lack goodness and are therefore evil.
If you think of it like that the Gray Jedi don't make any sense. Because like... What does it even mean in such a context? That they give to charity in the morning then kick a puppy in the afternoon to "balance" themselves? That they're merciful some of the time and ruthless others? That they're altruistic but also spend a lot of time psyching themselves up with rage so they don't lose their dark side powers?
Now I kind of want a satirical fic of someone attempting to be a Gray Jedi and living like that.
You don't need a satirical fic when this exact thing exists in canon. It's called The Clone Wars (2008) and shows Anakin living EXACTLY like this for about seven seasons' worth of episodes.