Valid point, especially considering the siblings are both over powered in the sense that the sister is a powerful fire bender with combustion bending (yay mind artillery) even if she won't be using it unless it's a actual long range thing, and the brother uses chi-blocking mixed with his air bending, however those attributes would also likely make them ideal people to be hired by the White Lotus.

Also I'm curious, what happens with spirit vine energy? Since you can clearly make it into a weapon I don't imagine everybody sitting by and letting it be rather than attaching their own variants to warships and airships, and if it turns into the Avatar equivalent of nuclear (Varik?) power than what's it powering by this point?