Your job is now to find a new job. Push as hard as you can on job searching. Dial down the effort you are putting into your current job. You absolutely should not stay where you are. You are also extremely unlikely to be able to make any positive changes there, the company product and needs “are what they are.”
I will try this. I unfortunately don’t really know how to dial down since it makes me feel guilty.
I know I often feel guilty if I feel I'm not giving my best, trying my hardest, and helping out as much as possible. That affects all aspects of my life, including but not limited to my job.
One thing that helps me with this guilt is when I have concrete evidence that the other party is not acting with the same worldview.
In this case, you're trying to do the right thing and help your employer, but your employer is not heeding your reasonable demands to be put on something else. Basically, they're not thinking about finding a "win win", they're only thinking about what's best for them. They reckon they can force you to stay on this project, which is best for them, therefore that's what they do.
Given that they're not making an effort to help you despite you asking them to, I think it's reasonable to not feel guilty about doing the same i.e. thinking about yourself first. I mean you're simply playing the game, where they have decided the rules, which is just doing whatever is best for the person taking the action. You did not force them to create these rules, they decided on that. And you're not imagining they have this mindset, they have demonstrated it through their actions.
And don't get distracted by words, look at the actions. They may well say "we're all team players, we help each other!" then keep you on this project. It might be tempting to believe the words they say, but their actions demonstrate their actual values.
That helps me when this sort of situation comes up, I hope that helps you a bit.