Obviously the noted "spoiler" objections are true for any historical fiction, so it does seem odd that they're a specific objection in this case.
"Spoilers" are also an issue for basically anything. "MC wins at the end, defeats baddies" describes virtually everything. Occasionally, you get one where "hero dies at the end, spectacularly", because if there's no meaning or interest in the hero's death, a story isn't going to be made about that. So you have two basic possible endings, coin-flip that and people seem upset if you tell them whether a particular series has Ending A or Ending B, despite this being about the most insignificant difference between stories.
If you were only watching movies "to see how they end", e.g. whether the hero lives or dies, then you're going to have a very poor movie watching experience. That's not what you're there for. "We don't see the wood for the trees" truly: we're not watching the movie to see whether it's an Ending A or Ending B movie, but to see what happens in between, yet we get the most upset about being told which type of ending it has.
But also, re-reading books I read as a teen as an adult, there are things I clearly missed because I didn't know e.g. as much about science and the world, or about male-female relationships, and where those are hinted at in the text I can now glean much more meaning from a few words from the author. So the reader's growth as a person can change meaning in a work as well.