It was really crowded Avengers Weekend. I've done 7 of the DL 1/2 Marathon Weekends which fall on Labor Day Weekend and 2 of the last Tinks which have fallen on MLK and this weekend was by far the busiest race weekend that I've ever seen. And this race only had 2 races, 1 Sat and 1 Sun where the other 2 weekends have 3 days of races and pretty sure more people running.
I got there 1st thing Friday morning and didn't have too bad of waits on the rides. Frid night I did the single rider for RSR after dinner and it was a 35 min wait and TSMM was the same. I went to DL and got there park opening on Sat and was in line for Jungle Cruise and it broke down so then moved over to Indy and that was closed and then POC was as well, so HM and Splash had longer lines, but that could happen all day of the year. I popped over to DCA around 11 or so and TOT was already a 40 min wait.
I heard 1st thing Sun morning was not bad. I got into the park around 11:30 and it was crazy insane. I've been the weekend before Xmas and honestly think this was more crowded. My dad had run a race in LA on Saturday so he wasn't 100% up for long lines and we did pop over to DTD after lunch, but we only did 1 ride and the train Sun. We could have gone on more, but the lines were pretty much all over 40/45 min.
The crowds were the combination of the race weekend and it being the 1st official weekend of the Xmas Season. I could see next year being the same, only b/c Disney races always sell out, and given the current trend and the popularity of the Avengers/Marvel theme, they'll probably add another race next year extending it from Fri-Sun which means a lot of runners will come in on Thurs instead of Fri.
Sorry it wasn't a better report, or crowd report that you were looking for.

If you are going for the atmosphere and decorations, I would say go and don't let the crowds deter you; I still enjoyed it, but I go a lot. If you don't go often and like to get on every ride, that weekend might not be the best.