How is this in any way shape or form the right setup for a BM hunter? A 23.74% loss of Mastery? SERIOUSLY?!?! I’m about to cancel my sub to AMR because the gear it keeps telling me to get is NUTS! Oh my toon is Sybrant on Azuremyst. I’m only looking at gear from 1st 4 bosses of Heroic ToS and 9/9 Normal ToS.
I would need more information to answer this. I need a link to your custom gearing strategy.
Which 4 bosses are you considering the first 4? Since you don’t really have to do all of them in an exact order.
I don’t think it is necessarily crazy to be losing some mastery. It could very well have to do with the items that are available from those bosses. Higher item level items without mastery might be available from those heroic bosses, which is resulting in less mastery, but higher item level.
Not sure if this is the link you need or not but here you go. Not Available
First 4 bosses are Goroth / Demonic Inquisition / Harjatan / Sisters of the Moon
The thing I don’t understand about the Mastery loss is that it’s recommended to have at least 90% mastery and mastery is the most important stat to a BM hunter, with my build, the zoo build as some call it, crit is very important too but not important enough to lose that much mastery.
There are a few different things going on here:
1.) 90% is not really a magic number for mastery. If you look at your gearing strategy, you get the best results with equal amounts of crit/mastery. There are not many combos of stats with more mastery than crit which are scoring within 1-2% of optimal DPS.
2.) With the options you have selected, getting 2pc t19 and 4pc t20 is possible, and the optimizer is doing that, which results in changing your legendary items. Doing some quick tests, this is definitely the highest possible DPS setup for you. The loss in mastery is largely incidental compared to picking up these set bonuses.
The optimizer is actually doing a really good job here as far as balancing out all the special effects like set bonuses and legendary items.
Ok, I’m going to go after this gear setup but I have my doubts. I feel I’m going to take a massive hit to my dps. But strangers things have happened. lol 
Keep in mind that if you were to make all the heroic gear in ToS available to you, the suggestions would likely change substantially.