Lets say there are 2 factions at war. One Evil and One Good.

Evil people can just ignore international laws and commit war crimes, Good people will have to abide by laws. Evil people can use torture to obtain information, while Good people aren't gonna use torture (because then they are no longer good by definition). Evil people can use chemical weapons and just attack indiscriminately, Good people have to make sure they don't accidentally attack civilians.

Good people are going to be against Nuclear Weapons, but Evil people doesn't care.

It seems like Evil is just more powerful. Do you believe that Evil is more powerful than Good? Why or why not?

I mean, we could have the "Good" faction starting to use Evil tactics, but then they aren't "Good" anymore, so the best we can get is a shadow of Grey, because truly Good people would just lose every time.

See Example:

Country A: Good

Country B: Half Good Half Evil

Country C: Evil

Country A would oppose nuclear weapons, while Country B builds them reluctantly (remember, they are only half Good), Country C builds them without any hesitation whatsoever. The result is Country A is doomed to fail, and an arms race between Country B and Country C. Good people always lose.