Caramelization is a mix of dehydration and sugar conversion. I've found that slicing thinner helps the dehydration process go quite a bit faster. Sugar conversion seems to depend on batch size (more onions = more time).

I suspect two things are going on.

The first is temperature. You can start low and go slow or you can start hotter and decrease the temp as you go to avoid charring. Actively controlling the temperature is faster, but increases the risk of accidental charring.

The second is your target state. You and the prior poster might just have different stopping targets. I personally keep going until it's nearly impossible to avoid charring and that takes me... quite a bit of time. By this point sugar content and flavor is maximized and highly concentrated. There's also a very substantial mass reduction thanks to evaporation.