Years ago a poster here named @Quasqueton
did an exhaustive analysis of available xp via gold and monsters in many of the classic 1e modules. I don't know if any of those old threads exist in archived form any more, but if memory serves the ratio of xp from treasure to xp from monsters was often much higher than 1:1, with sometimes as much as 80% of the available xp coming from treasure!
He also found that if one used xp-for-treasre as written the level advance rate per adventure in 1e wasn't much different from that in 3e, which came as a complete surprise to me.
It's even slower if you take out xp for treasure completely, as we did ages ago (and 2e did later).