Sacrosanct
Legend
OK, instead of guessing, let's get an actual visual reference. Looking at all monsters in the MM, it seems there's a steady increase in average AC by CR. I see a lot of people use this as a base reference point when doing their analysis, but it's not a very good way to analyze it because as the second chart shows, the actual AC is all over the board for every monster CR. You simply cannot predict accurately what a monster's AC will be based on it's CR. Secondly, not every monster is faced the same amount of times. Hence the second pair of graphs. This is just the humanoids, which are probably the most commonly encountered monster in the MM. When you look at that, the average AC values reveal a much different picture, and that's not even considering the very easy and realistic change the DM can do by giving those humanoids better armor and/or shields (which you can't really do to other monsters that can't grab or wear things).

