As a counterpoint, I have both 5.1 via ARC and Dolby Atmos system hooked up via eARC and dialogue is still quiet in some modern releases. Older movies sound great though.

this will be because more recent movies will be utilising high dynamic ranges for audio, worked around by compressing/limiting but in doing so, you lose quality.

trade-offs for everything.

there was a time when stereo was seen as unnecessary faff, too.

edit: movies are mixed for theatres and no longer are the home releases adjusted to suit.

In many cases, people ostensibly using stereo sound may as well be using mono sound. Stereo speakers built into a TV that's 20 feet away, or watching a video on their smartphone without headphones; technically these people are using stereo sound but with the speakers so close to each other relative to the listener, it might as well be mono.

I think if you want to make widely accessible audio content, you should be taking this into account. Make it intelligible in mono first, then worry about the rest.