I mean... you didn't even know Steam was a big deal. I figure you should trust the people with experience with Steam, instead of guessing how it might go. That's not doom and gloom versus naked positivity, this is experience versus dreaming.
I think people do check the Itch.io pages. You can even notify everyone who bought your game with the analytics options, so as to tell them about major updates/patches. And if they complain about bugs, when there is a patch you released on the main game page... then their complaints are truly hollow, and will ring so to others.
If you patched the game, fixed some bugs, and the balance of stuff like high miss rate and enemies that hit you with the parts you just destroyed, the major youtubers of the game would all be complimenting you for it, for responding to their feedback. They'd give a positive impression about the game and its development. They are dedicated people who keep track of updates and are part of the community, so they would notice updates and patches. As it is, we can only guess at how many people were turned off a purchase because of bugs in the let's plays.
By the time the update comes out, most of the LPers will have finished F&H. We don't even know what viewership the extra area you're adding will get compared to the main campaign. People like endings, so after Ending A gets posted on youtube, it's likely viewership will start to decline.
I think you shouldn't worry so much about little things like, "it's awkward to download a patch off the game page," and worry about the big ones like, "thousands of people are witnessing bugs in my game." A poor presentation on Steam is a big one, too; whereas releasing a couple of weeks later would be a small one.