Why it's impossible to drop Darkside (unless you are bad)

[Reynhart]

Normally if Darkside was still button you had to press like Blood of the Dragon I would agree... but it's more like WAR's Storm's... Eye? Or was it Storm's Path? Regardless you need to prepare the buff like DRG's Heavy Thrust buff... or even SAM's Jinpu or Shifu buffs... and the above mentioned are all GCD weaponskills and actually flow nicely into each other

It's exactly because they're not WS that it's so easy to maintain. It's also different from old BRD and MCH, because using a GCD to put your buff again was a DPS loss, so you'll try to delay it as much as possible. For DRK, it doesn't require any preparation to have the initial 60s window, and you also don't care about not benefiting from the full 30s increase so you can spam it for DPS.

The worst situation we should consider is if you have an empty MP pool with Darkside just above 30s (Unless you spend those last 3kMP on a non-broken TBN, while Darkside is nearly off, but in that case, I think "Get good" is also deserved). During those 30s, you can do enough combo + natural regeneration so you'll have access to a new Darkside skill. For Darkside to be something you really need to focus on, those skills should either cost far more MP, or extends Darkside for far less time, so that you don't have time to refill the cost during the timer extension.

Or, DRK should have another skill, unrelated to Darkside, you'd want to spend MP on (That could totally randomly be named "Dark Arts" and that could enhance some skills far more than the potency of Edge/Flood), so that you would have to decide if you can afford it or if Darkside would drop because of that.
Sounds familliar ?

Except that its 600 mp per SS.

600 is enough. In 30s of Darkside, you'll do 12 GCD, so 4 Syphon Strikes, so 2400 MP, and the natural MP regeneration will give you those 600 more MP during that window.
So, even if you manage to not have Blood Weapon nor C&S nor Delirium available during that "emergency" 30s window, you'll always refill enough MP to reapply Darkside before the previous timer runs out.

EDIT : Test on a dummy. Do a combo, use one Edge from full MP just after Syphon strike, then do your combo over and over. I got back to full MP with 9s left on Darkside.