I think you're carrying over some design assumptions from later editions which didn't necessarily apply to the earlier ones. Sometimes I do find things in the older editions which I consider genuinely BAD design. Sometimes those still make some sense in context and I can see the designers' rationale. And I don't think they were acting maliciously in limiting access to certain powerful tools and abilities, even if I don't 100% agree with their solutions.
One of the biggest problems people have, not just about D&D, but in general, is evaluating things from the past from the lens of the present. As you correctly note, the design assumptions were completely different. Heck, if you think that a single "hidden" ability is bad, how about these two feature... that aren't hidden?
For druids to advance from 11th level to 12th, they must seek out and DEFEAT IN COMBAT at 12th level druid. Same with going to 13th level. Same with going to 14th level. As for 15th level?
Assassins? To advance from 13th level to 14th, and 14th to 15th, you have to go to the heavily fortified headquarters of the assassin of the higher level and kill them. 16th level?
But that's nothing compared to the Monk. The 1e Monk was basically Gygax saying, "How about we make a class that I will both make totes OP like a Paladin, while
at the same time hitting it harder with my nerf bat that any other class. Yeah, thief, hold the monk's beer."
The Monk had to seek out and defeat a higher level monk to advance ... FOR EVERY LEVEL UP TO THE MAXIMUM LEVEL OF 17, starting at the transition from 7 to 8. That's right- TEN MORTAL KOMBATS!
Of course, the conception of rules was looser back then, so a lot of table didn't actually require this. But it's just different conceptions- first, tighter lore/crunch construction, and second the idea that tables viewed rules more "a la carte."
One of the debates about the nature of RPGs in the 1970s was whether players should know the rules AT ALL, or whether that inherently damaged immersion and ruined the illusion of experiencing a secondary world (see The Elusive Shift, if you haven't read it already).
Good to see someone else is banging the drum while I am mostly absent! Protip- get a macro for that.
Also? You need to start the bard hatin'.
The Elusive Shift is the path to the Snarf side.
The Elusive Shift leads to anger at soulless, dead-eyed elves.
Anger at soulless, dead-eyed elves leads to hatred of bards
Hatred of bards leads to making other people suffer through long and pointless essays.