When Blizzard implements new abilities they try not to just use a standard formula for how they should work. Different is fun and interesting. It is for that reason that we have DPS cooldowns like Invoke Xuen and Tigereye Brew. They are not just a boring "x% damage increased for y seconds on a z minute cooldown". They're unique.
In the case of Tigereye Brew there a couple major flaws in the design. The first is the fact that we start at 0 stacks so our damage is generally poorer in shorter fights and better in longer fights. The second flaw is the fact that we never build stacks if we aren't actively spending chi.
1. Starting at 0 stacks.
In PVE it is possible to workaround this by building stacks before the pull and using Tigereye Brew with your prepot. This is a hellish and annoying thing to do and is not intended. Assuming they fix this at some point that still leaves a disparity between our class where we have about 1 minute of "dead space" where we don't benefit from this cooldown.
In a 2 minute long fight we only get about 1 minute worth of our buff. But in a 10 minute fight we get about 9 minutes worth of our buff. So in the longest encounters Tigereye Brew can up to double the overall uptime compared to the shortest encounters. We are lucky this tier that there aren't many short encounters, but that's not something we can always expect in the future.
The other area this is a problem is in PVP. Most arena matches are determined in the first minute or so when both teams pop all their cooldowns and someone gets gibbed. We are useless in this area since we won't be able to pop our CD for the first minute at a reasonable stack count.
2. Relying on spending chi to build stacks.
Most DPS buffs work on a fixed cooldown. You can use them every x number of seconds no matter what.
This means in PVP it doesn't matter how much you get CC'd, kited, or whether you yourself need to kite to survive. Your cooldown will be up at the same time. In PVE this means that if there are times where you have to stop DPS, movement phases, etc., your cooldowns continue to count down while you are indisposed.
Tigereye Brew requires that we be actively generating and spending chi in order to use it. Any time we have downtime it hurts us.
I am not against this mechanic. It's fun. But I also think there should be some practical adjustment. I am not against keeping the 2nd flaw of Tigereye Brew, the part about requiring uptime on your target to build stacks. This will lead to strategy in PVP ("rotate CCs on the monk so he can't build stacks") and most PVE doesn't really have downtime anyway.
To fix the 1st flaw, my idea is to have a 5-min cooldown which automatically grants us stacks on demand. This would need to accompany a fix to correctly clear both the Tigereye Brew stacks and the actual buff when pulling a raid boss, otherwise people would continue to build stacks before a pull and would simply use this ability after the first Tigereye Brew wears off to chain them back to back.
The Perfect Brew
5 Minute Cooldown
Concoct a batch of your finest brew instantly.
Gain 10 stacks of Tigereye Brew.
Gain 15 stacks of Elusive Brew.
Gain 10 stacks of Mana Tea.
This could also be used in arena to perform burst damage right out of the gate. And it would remove our penalty for short fights in PVP.
The only balancing issue I can see with it is that it could be used to stack 4 Tigereye Brews back to back. Currently it is intended that we can stack 2 Tigereye Brews back to back, and by the time they finish we have at least 5-7 stacks (depending on haste) toward another 10-stack. Already this is kind of extreme, so being able to add an extra 10-stack would lead to some issues. Perhaps make it so that using Tigereye Brew puts a "shared cooldown" on this ability so that you can't use The Perfect Brew within 1 minute of using Tigereye Brew. Similar to how on-use trinkets have a shared cooldown so you can't pop them at the same time but you can still pop them on cooldown, you just have to stagger them and alternate.
I think Blizzard already recognizes this as a problem which is probably why they tried having Tigereye Brew gain a stack from only 2 chi. This lets us pop it sooner in arena (instead of not at all in some cases), but as we saw it led to horrible uptime issues especially in PVE. You can't have your burst ability with a >50% uptime. I think this is a better solution.