If you don't know whose side to take in a trademark dispute, one heuristic is: default to whichever side is trying to get the trademark invalidated. Because getting a trademark invalidated doesn't stop you using it -- it just stops you from using the law to stop other using it.
BTW, the key point in trademarks isn't whether there's prior use, technically. It's whether there's customary use, and (independently) whether the mark is purely descriptive. Widespread prior use is just evidence of those. (N.B. that's in the EU - I assume US law is similar, but don't actually know).
> I noticed the other day my pillow has a trademark on the word "Jumbo". Where are the people getting upset about that?
People are getting upset of this because they identify as gaymers - it's something they are. The word gets tied up with the identity. So naturally they get upset if someone tries to (from their POV) take the word away from them.