(granted, one could argue that the Russian leaders don't care how costly their victories are, meaning that the idea that Ukrainians don't surrender won't stop them from attacking anyways. But, even if the Russian leaders don't care, the Russian troops probably will, and that could have an impact on their effectiveness.)

Even if it was true, I'd disagree with the statement. Yes, on the surface it looks like they all died just to insult a warship. But, acting this way against superior forces, they help set a precedent that Ukrainian forces will not automatically surrender. This means that, even if an attacker has enough forces to win a battle, they'd have to weigh the potential cost of attacking knowing that they'll face resistance. Plus, like cake mentioned, propaganda value. All in all, if it was true, it wouldn't be a waste of their lives, but rather trading their lives for a broader goal. Whether one chooses to call that stupid depends on how much value one places on one's life compared to their cause.