It was about sick leave and improving the working conditions that are so awful that they're literally making workers sick and trains less safe.

every single source from the time, even directly from the unions, explicitly discussed only paid sick leave

That's simply not true. That's the MSM and party narrative, but it isn't the truth. Outlets less intertwined with the political establishment such as The Intercept and The Nation could have informed you better, had you bothered to look beyond the bubble.

in that sense they got their demand met completely

You mean in that entirely fictional sense? To quote the Nation piece:

this was never just a conflict over the number of paid sick days. About 115,000 workers represented by 13 separate craft unions, who keep 40 percent of the nation’s freight moving, got screwed. The coalition of interests that did the screwing includes: the executive boards of the seven class-1 carriers, most of Congress, and the president.