I used to be able to understand 99% of the dialogue in Hollywood films. But over the past 10 years or so, I've noticed that percentage has dropped significantly — and it's not due to hearing loss on my end. It's gotten to the point where I find myself occasionally not being able to parse entire lines of dialogue when I see a movie in a theater, and when I watch things at home, I've defaulted to turning the subtitles on to make sure I don't miss anything crucial to the plot.
I found the linked article interesting. I do have terrible hearing but I now use good quality hearing aids that are set to 40% volume. This works fine in almost every circumstance, other than for movie dialogue. Even setting my hearing aids to 100%, which endows me with bat-like hearing in normal life, doesn't help with movie dialogue.
Sound-effects, such as explosions, can be deafening, but dialogue is often too quiet.
I use subtitles by default anyway, but I still like to hear the dialogue if I can. The remote control is glued to my hand watching an action movie. I'm constantly raising the sound during the quiet parts in order to hear the dialogue, then lowering it during the action scenes to make sure my eardrums don't evaporate.
As the article indicates, it's not as simple as raising the volume of the dialogue at the mixing stage.