Gandalf a "steward?"

[Legolas]

"once again inaccurately" - what does that mean?

It is accurate. Try reading it again.

Yet it is not our part to master all the tides of the world, but to do what is in us for the succour of those years wherein we are set, uprooting the evil in the fields that we know, so that those who live after may have clean earth to till. What weather they shall have is not ours to rule.

He is asking that everyone be stewards of Middle-earth - not to be great generals of countries, but to simply take care of the world whereever they are.

steward - one who manages another's property, finances, or other affairs