Very quick napkin math regarding set bonuses.

Assuming stagger is always ticking on you, on average the 4pc BM set bonus gives you one free chi every 10 seconds (which can only be used to PB).

2pc WW on average gives 10 energy every 6.67 chi generator, which all cost 40 energy (ignore CJL). So after 26.67 attacks you've generated enough bonus energy for one extra chi. Assuming 15 energy/sec regen, that would take 72 seconds.

Not really a contest, assuming you are staggering damage. That said, BM bonuses look REALLY good. With the mastery buff, if you went for like 15k mastery with t15 gear, you'd be approaching 90% stagger with fort brew and 2pc up.

I think that 2pc may change the way we use Elusive Brew. I'm not certain on that, mind you, but if we use EB at 5 stacks, that's 5 seconds of EB and 5 seconds of 2-piece with only a 9-second cooldown on EB. I don't think current gear provides crit chances that can quite support 100% uptime of EB/2-piece, but it may be possible next tier. If that does become a possibility, this will provide significant damage reduction over the course of a fight.

With secondary stat values increasing with item levels inflation, 4pc t15 providing a free PB every 10 seconds (kind of), and Chi-based heals now being free, maintaining 100% Shuffle uptime should be the easiest thing in the world come 5.2, and 2pc t15 creating another buff to struggle with managing 100% uptime on is a mechanic that should prove rewarding and potentially challenging.

4. 2T15 increases value of crit for BMs until EB's uptime reaches 50% in the long run. Afterwards it's value should be lower. Still higher than it is now, I guess. After buffs to mastery and removal of T30 Chi cost, I will have a chunk of stats available, and now I know where to put them

Yes. Well said, I think the most basic mathematical analysis for this 2pc is that it puts a soft cap on the value of EB at 50% uptime. It also obviously improves the value of critical strike rating as a damage reduction statistic.

Now, what crit change is required for 50% uptime? That is a function of weapon type (which controls EB procs per crit) and swing speed. Sticking with simplicity, let's say it's a perfect 2.0 swing speed with a polearm, so 3 stacks per crit. To achieve perfect uptime, we need to land two crits every twelve seconds. Two of every six attacks must crit, meaning we need 33% crit chance, plus another 3% to make up for crit suppression on bosses, so 36%. That's actually not a high value, but it also assumes perfectly even spacing on crits, which is a completely unreasonable expectation.

So, I feel that, if you have a perfect 2.0 swing speed, aiming for ~36% crit is the minimum value of crit to shoot for once you have acquired t15 2-piece. Now, once weapon speeds shift around, that's where it gets murky.

There's math to be done.