Depends on the mirrorless camera, doesn't it? The smaller ones are hardly bigger than larger smartphone, and they do offer way better picture quality.
I can stick my iPhone 7 in my jeans pocket. My Olympus Pen-F (one of the "smaller" mirrorless cameras) with a small prime lens needs a pretty big pocket only some of my larger coats have. Plus it's heavy enough to pull on said coat and make it uncomfortable.
Yeah, image quality is pretty bad on the iPhone compared to the Olympus. But when I go out and about and don't want to have a bulky thing hanging around my neck / forearm or carry an extra bag, the Olympus' image quality is exactly 0. The iPhone beats that hands down, even at night.
Now don't get me wrong, I love my pen-f, and it's an incredible improvement over the DSLR I used to haul around before. But iPhones are getting pretty good for my needs now.
Now I am thankful my dad endured the pain and captured a lot of stuff on the JVC shoulder camera. At least the quality is pretty good even for 80's/90's.
We don't capture events like we used to anyway. No one holds there camera up for more than a minute. So we're left with all these short videos. I like watching the really long stuff my dad shot.
Also, most DSLRs these days have some sort of multi-exposure functionality built-in. Sometimes it's as simple as 'bracketing' (so you get multiple phones you have to merge together in post), but some fancier ones offer HDR functionality in-camera, so nothing to do in post.