You constantly conflate things and can't tell the difference in what is being talked about. Planning with travel guides in the 80s is nothing like the 'planning' people are talking about where people are locked into parks, dining, and rides months in advance.
We used the official travel guides from the start (1981). The travel guides were helpful so you knew what was there, what to expect, and to help you plan your trip. But yet, we didn't lock ourselves into hard schedules 6 months in advance. We didn't have to reserve every major action you went through.
The consequence of not planning back then was more about 'not knowing something was available', or understanding the visitation patterns, or maybe missing out on that table service that day because you didn't know how bookings were done. Even in later years where other guides started coaching more on how to optimize your visit to minimize crowds... we're still nothing like what is being discussed here with FP+ vs Genie+.
Back in the day 'planning' was about KNOWING what was there and gaining familiarity so you got the most of your trip. There were no websites to prep you, no youtube tours. You read books to know what the offerings were. Planning was about knowledge of the product so you could focus on the things that interested you -- and less so about avoiding waits. That was just a smaller piece of things. Because then it was more about knowing crowd patterns, and insights that may not be as common knowledge to the general population back then (like riding during parades, etc). It was more about TIPS and insights - It wasn't about creating minute by minute or step by step movement tables like things have become as people try to optimize everything to death.
When it was only 2 theme parks.. you didn't even goto the parks every day necessarily. Disney has been pushing the "gotta see it all" and commando scheduling for over a decade now and it's become a monster.