What is the college doing with regards to the withheld grades?

Even if they did average all my other work, I'd be pissed I put all that effort into something that has zero impact on my grade.

You're acting like the grad students have clean hands here which is clearly not true. They joined the union with the intent they would negotiate on their behalf. The union did so and promised to stop any wildcat strike. The students didn't like the job the union did, so they went on strike, violating the contract.