when I was playing I was a hardcore mythic raiding schedule so YES IT WAS A WASTE OF TIME because you need to farm your mats, always try and get the BEST gear to not get sat, be farming artifact power for AGES in Legion, and then sit 16hrs a week doing the raid. Then clear heroic, do alts incase a person is missing. hardcore mythic raiding was like a part time job. OF COURSE it’s not a waste of time if you’re just doing it as a hobby or casual dungeons.
So yes, that’s why they were a waste of time for me.