We use a unique method for evaluating healing gear: Simulation. Right now the Raid Healing gearing strategy is based off of the Vectus encounter in Uldir. We simulate and account for many more variables than you can without a simulator: Some examples are: real damage patterns, the other healers in the raid, the damage reduction that you get from Versatility (that’s free healing!), etc. This often leads to significantly different advice than what you see from other places that are using a less complex model of the game.
Here is a 4 part blog series on our methodology: http://blog.askmrrobot.com/healer-sims-part-1/
Regarding Autumn Leaves in particular: For that trait to be considered the best trait, it would require a significant alteration to play style in raids. I will take a closer look at it and see if altering your play to leverage it more can end up with it ranking higher. It really kind of works against mastery to some degree though… which limits the power of it. Also, I’m highly suspect of stacking three of one trait when you have a trait like Waking Dream available. The portion of that trait which lowers the interval to 4 sec is strong and doesn’t stack. Having one of that trait is going to be very worthwhile, just as an example.