Things became worse in the past 10 or something years (I am a 40 something btw.). As the article states we used subtitles in movies to learn language and to understand thick accent. However throughout time while we got better and better in comprehension the use of subtitles remained the same in overall. But very uneven too.
Old movies (not yet seen) and movies for children are never a problem. Also some properly made movies. The atmosphere and sound effects are fine as well as the dialogs.
But it became too much of a trend to make muttery a mushy dialogs where people seemingly unable to articulate. To the level never heard in real life (where muttering may be more common due to the more causal and mood or situation affected nature of conversations, unlike the carefully created and heavily controlled ones in movies). Also it is uneven. Some movies are still fine, but others (perhaps the newest Batman comes to mind, unsure, forgot that movie mostly, being so obscure) are a struggle, not fun at all. Aggrevated by the loud bangs and muttery dialog combo.
A sign that this is a systematic and intentionally manufactured problem, that sound engineers and directors lost their touch completely, is the existence of a feature in the newest Apple TV for equalizing the sound level in a movie. Streaming hardware manufacturers had to come up with solution to correct what sound engineers ruined or unable to get right nowadays.
Older movies are almost never a problem. New movies are in an uncomfortable amount.