I was playing around with the d100 Unusual Thief Abilities table by the prolific creator ktrey, and thinking about its various uses. The B/X thief abilities existed not only to emulate a particular kind of character but also to define the game they were made for. These early D&D thieves have abilities like "open lock" and "find and remove traps" because those are the abilities that many early D&D games necessitated. If there were no thief class, we might imagine that there would have to be fewer traps and locks in dungeons or that rules would have to be added to allow people to have a mechanical procedure for addressing those challenges in a similar way to how the thief class would.
This reminds me of the later principle called niche protection, the idea that the system of the game should not only give a class certain abilities but ensure that other player characters cannot perform the same category of ability well. While I feel like niche protection became a talking point in the more build-focused style of play that meant people were more likely to feel outshon in play by their friend's meticulously designed character, early D&D certainly has forms of niche protection.
Only a thief gets a procedure to open locks. Only a fighter can use a magic sword. Plenty of considerations like that. One difference is that the game (cum fide) assumes that a PC is competent in all general adventuring practices, and this is actually a great consolation. Even if you don't have the thief's trapfinding ability, at least you don't need to roll a die for every five-foot square you probe with your pole.
Another difference, it must be said, is that the philosophy of niche protection is not drawn out to its fullest extent in classic D&D. Consider all the reasons that you need a thief to pick a lock but you don't need an elf to find a secret door. I'm not sure that any given edition of classic D&D gets niches exactly right, but it really does feel like a considered design decision.
Finally returning to ktrey's unusual thief abilities table, it sparks my imagination simply because it leads me to think about the games and game systems that would feature them. It's not every campaign where timing fuses or bootlegging is as central as opening locks. I wonder also at how the game is to be played if no PC can pick locks or perform some other typical thief ability. The relationship between a class's abilities and the shape of the system must always persist. and each must be apt for the other.
For your consideration, ktrey's table turned into a table with Spwack's html tool: