There's a considerable amount of content on the Wiki that some would consider "irrelevant", but I wouldn't call this bit of information you're trying to remove irrelevant.
Both related shows are relevant in animated pop culture as of the mid to late 2010s, and a number of users (both here and on other social websites) have pointed out the similarity, so it holds at least SOME merit.
If there ARE any other notable bits of trivia that can be added, they could be added accordingly. Until then, I still see no reason that the trivia point related to MLP should be removed.
What about the Teen Titans trivia on Globgor's page? Or the Gravity Falls trivia on Glossaryck's page? Or the multiple pieces of trivia related to various magical girl anime on Star Butterfly's page? What grounds for removal is there for any of that?