For sure people were building strength before organized and labelled routines were popular, but it's not about the brand name, it's about the underlying principles. Other than genetic freaks who can build muscle and strength from absolutely anything, there are almost always common threads to the training of all successful lifters.
I disagree to an extent. Autoregulation and adapting for individual variables is one thing, but a 43-year old mother of twins, a 32-year old accountant, and 21-year old lacrosse player could do the exact same program and get relatively-comparable results, as long as their goals are the same (obviously) and as long as they can handle the given workload. Programs get "popularized" (for lack of a better term) because they work, repeatedly, on anybody for whom the program is appropriate.
I'd just like to point out that four or five of your six personal principles are absolutely in line with 5/3/1 training. Looking at it from another perspective, I'd also say that five of your six principles are absolutely in line with traditional Westside methods. If you were born 70 years ago or born today in North Korea with no Internet and no library, but still came to the same conclusions about your training, doesn't that say some about those principles? There just might be more to "fancy programs" than you're realizing.
The most successful plans have more in common than many recognize. Like the old saying goes, get 10 top coaches in a room and they'll agree on 90% of things. Get 10 amateurs in a room and they'll argue about 90% of things.
I definitely agree with this. Unfortunately, it's now profitable to overcomplicate things for the sake of sounding qualified. I think it's especially an issue with the generation of Internet-grown "trainers", who are most often just guys who've built good bodies for themselves (and a large Youtube/Instagram following) with little to no actual experience training clients.