You're still missing the overarching point. Why is it good design to have people do not fun content in order to get to fun content?
And yes, some of us are forced to do the not fun content in order to do fun content. This isn't even a debatable point. If I want to progress in mythic raids, I must do Torghast every week. No ifs, ands, or buts. No group pushing mythic content will accept someone with 0 legendaries, and no one would want to join my mythic progression group if I have 0 legendaries. So, no, I can't just "do the content I find fun."