Marshal Lucky said:
Type the words "13th Warrior" and "Seven Samurai" into the Google search bar and look at the results.
Now that is interesting. I still haven't found any of them saying why one is inspired by the other, but at least now I know you are not alone.
But even if the one movie was inspired by the latter, which frankly I am not convinced of yet, "inspired by" is not the same as "lame rip-off" of. The two movies are quite different. For the list of "similarities" you give (many of which have been challenged in this thread) there are equivalent lists of "differences":
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Seven Samurai has no foreigner learning about a strange culture (and the members of that culture learning about the foreigner - which ranges from their initial derision of the "toy sword" that the Bandaras character has made, to the warriors' leader appreciation of the ability to "draw" a story to remember the tales of a hero, for example), which is a major point of
13th Warrior.
-The former movie has no equivalent to the "bandit's mother" or "bandit's permanent lair", and no slow-acting poisons (leading to a rather inspiring speech at the end).
-There is no "are they are aren't they?" question about the supernatural nature of their bandit foes in the former movie, like there is in the latter. The bandits in the former movie have no religious or cannibalistic overtones.
-As stated above, the reaction of the "love interest" by the rest of the villagers was *very* different in the two movies. And
Seven Samurai did not invent the idea of strangers having romantic encounters.
-The gathering of the warriors is very different in the two films, with one taking seconds and the other one going through a long process of finding people (and getting rejected by at least one).
-Dealing with discord in the village (directed at the protectors) is done very differently in the two films. One's solution is through talking, and the other through violence.
This leaves us with the "leader that seldom speaks", "each member of the group having a speciality", "defending the village with stakes and such" and "the slow motion battle in the rain of few on foot vs. many mounted".
The first one is a common trope: "stoic warrior". That is older than
Seven Samurai and I see no reason to think the influence came from just that one movie. The second is a necessity of making any movie about a group of otherwise similar people, so that the audience can keep track of who is who. That would have been in
13th Warrior whether or not
Seven Samurai was ever made, because it has to. The third is just a common sense realization of how to defend a village vs. attackers. Castles have moats, villages have palisades. That idea is far older than movies are, and there is no reason to expect that one movie only got that idea from the other.
The last one is possibly convincing, since you have a lot of separate events coming together. "Rain", "On foot vs. Mounted" and "Slow Motion". So I could imagine that *this one scene* was inspired by a scene in another movie, but that is about it. And many movies do that. A kinder word than "rip off" would be "homage". And, on the other hand, I could also believe in parallel thinking.
I liked both movies, but don't see the case you are making as convincing.