Shannon,

You're in an exploitative busines relationship and you should get out of it quickly. If the contract will be finished in the near future then it may make sense to stay the course until it is done and then refuse future contracts. If not, then the situation you are in is not a unique one. Many freelancers on Upwork have probably faced similar circumstances: I would recommend simply googling "Getting out of an Upwork contract without getting a bad review." It will return some possible leads (I know because I just checked).

I'd also encourage you to Google text and key phrases for the pieces you wrote for this employer to see what they're doing with it. At the very least it will help you learn a bit more about the industry.

As for what I would accept, like you, it depends on the point I am at in my career, along with what my goals are and what the norms of the industry I am doing work for are. I really don't have a way of answering you because of my own lack of experience.

I wouldn't work a freelance job where I felt like I was clearly being cheated or devalued though.

The stuff that you described, by the way, such as the difficulty of the assignments slowly ramping up? That sounds like someone who is well aware that they are exploiting their workers, to the point where they have strategized ways (like gradual increase in difficulty) to keep them on the leash for as long as possible.

J