I just saw The Hidden Fortress for the first time last week. And I have to say, it had almost nothing to with SW. If people hadn’t been saying it from the beginning, I wouldn’t even have made the connection myself. Pretty much the only thing is bickering soldiers that resemble R2 and 3PO (which is an insult to the droids as these people are just immoral scum to the very end), and there is one scene that is almost exactly the same in SW than in THF. Other than that, I don’t see any other similarities other than some ideas like there being a general and a princess, but you can find similar architypes from many movies. The plot is completely different and so are the characters. Comparing it to SW took me out of the movie a bit since I kept waiting “is there going to be this and this scene next” and there never was.
I don’t think anyone is saying Lucas copied the plot, just the bickering peasants bit.