I think it's fairly limiting to only look at the last couple of months seeing as X-Men didn't even release an issue in April, and this Avengers arc has had a lot of third party interest due to characters wielding the phoenix force (an X-Men creation) - not to mention it features way more characters than just the Avengers (Echo, Wolverine, Namor etc). If you look back through the end of 2019 through 2020, X-titles are pretty consistent in their sales - beating out Avengers and pretty frequently going toe to toe with Batman and Spider-Man.
I also think Covid had a bad effect on the X-Line - any body who was buying multiple titles have likely had to cut down due to lockdowns/redundancies etc. I don't know if comichron tallies international diamond sales but I know Europe's comic ordering has been all over the place due to the constant lockdowns.