So I have a question for you. Out of curiosity, what was the reason for not changing masteries for Season 5?? Too busy with other changes, or just that the masteries are still good for another season or two, or what??
Few reasons, on the value side updating the trees has increasingly less value each time we do it. Not saying there isn't value but it gets more and more into small scale numbers tuning (or in mastery cases REALLY small numbers tuning) and less about solving largescale problem. This isn't terrible surprising as when we approached them initially in Season 2 it was a pretty substantial overhaul, the S3 and S4 updates while certainly improvements were more on the lighter tuning side of things.
In addition, the cost of doing this adjustment is really high. We need to wipe all players mastery pages each time we do an update beyond a very simple balancing change which based on a lot of player feedback is something people don't want to go through unless there are really substantial gains.