To me ALL of these are train wreck laundry lists of how NOT to write HTML much less CSS.
If you have enough CSS for a normal website to need seven separate scripting files, you likely have too much CSS and/or don't know enough HTML or CSS to be writing either in the first blasted place. This stems from the fact that 99% of websites have ZERO BLASTED EXCUSE for more than 48k of CSS in one file per media target...
... assuming the developer even knows what media targets are and what the media="" attribute does. Which of course rules out the know-nothing derps who use idiotic trash like bootcrap or tailwind.
OOCSS is fine if you bother leveraging selectors and combinators instead of pissing in presentational classes from so on-high you'd think the almighty just got back from a kegger. Comically and tragically so when people who advocate it talk about separation of concerns, and then use it to do THE EXACT FLIPPING OPPOSITE!!!
The classes in your example being a poster child for this nonsense and is why ... well, that next section is even worse.
Because BEM is 100% pissing classes onto everything for NOTHING.
And don't even get me STARTED about the nonsensical halfwit TRASH that is presentational classes. If you're going to make classes like "btn blue" or "btn-light-blue" (on DIV that should be BUTTON) please, for the love of Christmas, admit defeat and go back to writing HTML 3.2 with all those CENTER / FONT tags, ALIGN, BGCOLOR, COLOR, BORDER, SIZE attributes, and tables for layout you all so dearly and clearly seem to miss.
All of this just strikes me as more of those hot and trendy 3i of web development: ignorance, incompetence, and ineptitude. Systems CREATED by people who simply don't understand HTML enough to be applying CSS to it. Worse, a favorite of those who have their craniums firmly wedged up 1997's rectum in their desire to recreate EVERYTHING that was wrong with HTML 3.2 and 4 Tranny.
Just like the mind-numbingly dumbass nonsense that are HTML/CSS frameworks.
Whenever I see these types of articles all I can think is "LEARN HTML!"... 'cause if you actually knew and understood HTML and CSS, you wouldn't be so easily saddled up and taken for a ride by the know-nothings who peddle this type of nonsense.