Yeah, spending hours on it is definitely not out of the ordinary, it's such a ridiculous final segment. Which is tragic because the rest of the game is definitely "tough but fair", they piled the nonsense high at the very end of the game. Another thing that's better on the NES version is the hitbox on Samurai Guard - his hitbox is so goofy in the arcade version. And since the Japanese arcade version (the one that's on PS4) has shorter time limits, there are cases where I've actually Time Over'd on Samurai Guard because I am just not able to hit him, haha. But it's fine in the NES version.
Another Irem arcade game I've never 1CC'd is a side-scroller called Ken Go. It's a super cool game, by the way, which unfortunately never received a home release, but it's rock solid. Once again though, the final stage is nuts and always takes me a continue to survive, even if I get there with a full rack of lives.