Now THIS actually WAS universal--assuming you weren't cheating!
Depended on how long and regularly you played. It was absolutely a slog, but when you were playing all the time, often two characters at a time, it was entirely possible to at least hit the low two digits. You might have gone through more than a couple characters getting there though...
Define cheating.
I encountered some munchkins (in the literal sense of much younger gamers) with like 30th level characters. But the way that had happened was they had never played an adventure per se. Rather, they had a group of 2 players and the DM would select a monster from the MM's and then the player would fight it, get treasure and full XP for the combat, and they'd rinse and repeat. For hours. For days. For whole summers. As the PC's leveled up, they got overgeared and OP compared to the sort of things the DM was throwing at him. They'd moved on to creatures in the Dieties and Demigods by that point.
But they had no dungeon crawling skills, had never encountered movement or, terrain, or traps, or reinforcements, or attrition, or really anything we'd associate with the experience. It was probably something like playing 5e with a long rest between each fight with each fight being slightly under leveled. They'd had a lot of fun playing, but also at the same time it was obvious they didn't know how to play.
Yeah, I would say it would be near-universal unless
if and only if you played 'by the book' --both RAW and without deviation from designer intended play loop. Also, if everyone gets the rules wrong (say, because you started playing at age 8-10 with other kids that age and no adults steering you to the correct reading of the rules*), is it cheating or some other term?
*pretending for the moment that adults would always get the rules right with some of those rulebooks.
I know when we started, we interpreted monsters with 'no. appearing' of 40-400 to mean that you got one iteration of the treasure table roll per 40 appearing ("no way ten times as many goblins would have the same treasure!"). So if you broke a dam (with dynamite, which they totally had in medieval times, since 8-10 year olds don't know otherwise) and flooded an advancing goblin army, you got massively multiple rolls on the treasure tables (and gp=xp, we figured that out quick).
Likewise, if you find a dragon egg and hatch it and raise it to be an adult dragon, it can lay eggs for you and you can start a dragon egg business and the DM has to come up with the monthly income of that (and that income counts as xp too, right?).
So, yeah, we played wildly outside the rules as written (we also did some that would have benefited us, like completely missing the -3-+3 bonuses from high attributes in B/X), but I don't think I'd say we 'cheated.' We just got things wrong, and did things for which the game system didn't expect or account.
And while there will always be a previous generation that disdains the tastes of the current generation, that doesn't make them right. Even when D&D was first created in 1974, there were older wargamers that derided this new-fangled heresy.
And when
Chainmail was released, it was derided by some/many historical wargamers for having the fantasy supplement. The hobby has never had a lack of gatekeepers trying to declare a new angle on the thing lessor than the way that came before.