>>4223438MP is a tool. More MP reduces aliasing without fucking anything else up, there's a minimum you need to "crop for reach" with good quality, and allows you to trade resolution for strong noise reduction, so high megapixel cameras actually do better in low light. XT4 to XT5 is good for using an extra stop of ISO if you aren't using 40 megapixels of print size.
But like any tool you can buy today, it quickly gets to a level where what would have been massive improvements a long time ago are barely noticeable, like the ones and tens in a five figure price tag, and only autists with no real world experience are left caring about it.