I've been doing Mythic Blackrock Foundry on a few characters and I must say, it's far more enjoyable not slaughtering the bosses within 10 seconds. They usually take me 2-3 minutes depending on the fight as a pretty casual player, not a min/maxer by any means. Also you rarely take any damage, but there are certainly some mechanics and fights that will kill you if you don't put at least a little effort into it. I understand a lot of people enjoy soloing old raids for the mindless spam fest to get collectible gear and mounts very quick, but I find this current difficulty of Mythic BRF the sweet spot for soloing old raids.
This is how it was back in Cataclysm and perhaps MoP before the legacy scale Uber-damage buff happened. I absolutely looooved soloing old raids back then because they presented at least a tiny bit of challenge. Just my opinion! Let me know how you guys feel.