Yikes man…That’s way more than “not ideal”.
As far as Boltaction saying it only helps on the pull, I’ll prove you wrong.
Currently, my tank gear has me at 1101 Haste (16.19%). This puts DS recharge time at 17 seconds with a fixed 6 second duration. Three stacks would allow for 100% uptime. There is precedence for this via Leg slot legendary in Legion giving a third stack, and monk’s ability to keep their brew up 100%.
At 0 seconds I pop DS #1; cooldown will come back up at 17 seconds. It will expire at exactly 6 seconds, where I can pop DS #2; cooldown will come back up at 23 seconds. At 12 seconds, DS #2 expires, and I pop DS #3; cooldown will come back up at 29 seconds.
At 17 seconds, DS #1 has finished its cooldown while I still have 1 second remaining on DS #3. This would continue with having a ~1 second elapse where you have DS running and a charge available to use.
Also, perfect timing is not required because if you use DS with another charge active, it adds precisely 6 seconds (no pandemic, just full duration) onto the buff. You could, theoretically, spam all your charges and have an 18 second buff (minus time for GCD).
Now, this might be a little bit over tuned at this point. Currently, my DS changes my armor from 3679 (36.87% DR) to 10726 (63.00% DR) and increases my parry from 11% to 26%.
They could pull the Armor gain down 10% or so and maybe the parry down a couple of % to account for 100% uptime. As it is, if DS isn’t up, we’re gonna get thrashed, especially on fortified weeks.