I doubt this. More likely, in fact, is that if you are attracted to one MMO, you are likely to try others as well. I know that I played WoW from 2008 to 2018, and I've played BnS when it came out (and GW2, and Rift, and Wildstar and ...). I started FFXIV in 2014.
The others don't compete for my funds, they complement each other -- when one is in a lull, the others are there to play.
Your comment about over-leveling content belies the title and reason for the OP post -- which was that there wasn't enough XP.