It tends to go up over time, and candidates tournaments tend to have higher average ratings since the lowest rated player is ~2700 and wont bring the average down.
Which is to say... you say you think there are tournaments with higher averages, but probably not. This year is probably in the top 3 if not #1.
The average for this year's event based on current ratings and with the assumption that Ding Liren will be the replacement for Karjakin is 2776.
Have there been higher averages for the candidates? I'm sure there are tournaments with higher averages but I'm just curious about the candidates.