To be fair, you can have a hyperminimal UI without also being limited to a hyperminimum of available information.
On WoW, for instance, my only visible UI outside of combat (areas) was my mini-map, a line of buffs (filtered) at the bottom-center of my screen, and a minimized party/raid list. The last appeared as simply portraits and a counter; those within 80 yards got portraits, increasing slightly in size until within 40 yards, while the rest were reduced to a +<n> counter. Mousing over the area would expand it to show all others, so I could easily right click on them for whispers, promote them to leader, etc.
When they were in combat (areas) or when their HP was below 95%, a segmented circle border would form around their portrait, each segment equal to an amount of HP, so that I'd effectively have visual indication of both %HP and true value. That border's color would transition fade from light green to darker green to gold to orange to red for better at-a-glance reading.
Once an enemy was selected or I was in combat, I could see my on-cooldown CDs and my 5 core rotational skills, an enemy HP bar, name, %HP, and abridged remaining HP value. These on-cooldown CDs would appear below the rotational skills, centered and forming two rows for role-centric (Primary) and utility (Secondary) CDs. Refreshed CDs would flash (with color based on CD type) and linger a brief moment to better catch my eye, but I otherwise just understood that if they weren't on the list of things on cooldown, then they were ready to go. A couple high priority CDs I'd also have move to the top of the bars and glow upon refresh.
Mini-menu? Flyout from the right, now with larger buttons and some further shortcuts. If I were able to change jobs or had further reason to swap gear-sets on the fly? Would have been a fly-out from the left.
Thus, in total, I'd have all the information I needed for my 25-28 skills (depending on spec)... with only 5 persistent buttons showing on my screen, while being just as readable, after a couple hours getting used to the new layout, as my old brick hotbars (a 3x12 layout keymap I'd copied over from XIV).
My monitor (3440x1440) has 4,953,600 pixels. My personal combat UI, in total, took up a little under 4k pixels before procs/CDs, and around 5.8k pixels at most, despite using large, highly readable icons. The party list, with or without buffs/CDs (tracking just a few core CDs from each spec), took up another 6.2 to 8k pixels. The minimap was the largest expense, at another 32.4k pixels. Details, if I was running it, would take up about another 14k.
In total, though, my UI covered barely some 1% of my screen. It was incredibly readable, gave me what information I needed (and M+ tends to want more information than anything in XIV), and was still quite minimal / uninvasive.
Now, all that is a matter of combat UI, rather than, say, guiding players towards Recommendations, Challenges, Daily Roulettes, etc., let alone providing in-game guides, additional information like how various gear is stat-ed or look and where one can acquire them, and so forth, as nicely put together through WoW's Adventurer's Journal, but the idea that having a solid amount of information would necessitate a claustrophobic, UI-ed-to-death mess seems a failure of imagination.
(And the thing that was so nice about addon support like WoW's, was that one could tailor absolutely everything to their personal preference.)