Yes, there’s a direct correlation between a viewer’s time on site and the number of ads shown, even for YouTube. For example, let’s say YouTube showed a pre-roll video ad once every 10 minutes of video consumed, and let’s assume under that circumstance the average viewer watched 30 minutes of video. If YouTube increased the frequency of the pre-roll video ads to less than 10 minutes, they would expect a decline in the total amount of time the viewer spent onsite watching videos from 30 minutes.
The YouTube monetization team monitors these numbers very closely to make sure there isn’t a significant drop in video consumption. If viewership starts to drop, they will quickly adjust the frequency algorithm.
They are also working on new features to reduce the impact of ads, such as the one I worked on 
One caveat to this is that individual YouTube channels can control their own ad frequency and the type of ads they want (e.g. pre-roll, Ad Skip, banner), so some channels may have higher ad frequency than the YouTube standard.