It's... sort of unreliable.
Back in the early 2000s, we had a series of threads examining the amount of XP and treasure in the early AD&D adventures, and the totals indicated a very similar levelling speed to that of 3E.
But, and this is a big but, we're also aware that a lot of early groups got rid of XP for treasure in the early days. (That faction eventually came out on top in AD&D 2E and relegated XP to treasure as an optional rule). In theory, story-based XP was meant to replace it, but AD&D 2E's guidelines made that a lot less than the XP for treasure. (As I recall, it was capped to be equal to the monster XP, so instead of the 20% monster/80% treasure split, you became 50% monster/50% story, which given the same number of monsters, meant level gain was more than halved in frequency). Did those early gamers make up the XP, or were they happy with slow level-gain?
By the time of 3E, it's mostly all monster XP. And by 5E, the designers seem to like "DM gives out levels when they think appropriate".
In the case of the D&D Adventurers League, where an ongoing DM is not assured, it's possible under the current rules to gain a level after every 2-hour session! This isn't how 5E works in most homes, however!
Going back to the "old days", you also have the Monty Haul gamers. Anyone think they were going up at slow rates?
There is likely a "typical" group, but I'm not sure that even the folks at TSR were really aware of what that was.
Cheers,
Merric