Frodo made plenty of mistakes in LotR. Of course, you could argue that most of those were under the influence of the Ring but it's by no means as clear cut as you make it out to be.

I don't think your definition of gritty is correct either. What you describe seems more like realism to me. Gritty takes it further by adding more violence and unpleasantness. It's not so much about shades of grey.

That said, "gritty" is a completely overused and thus meaningless phrase, in my opinion.