Yeah rpg sourcebooks (mine are also WW) are not a good fit for the remarkable.
In general, only short PDFs are bearable, epubs feel like they should work but they take an incredibly long time to render, which frustrates me every time.
That being said, it's absolutely incredible for writing, but I don't need that as much as I used to (take less notes now as I'm more of an IC than my former team lead/PM/IC hybrid).