OP, you seem to be mistaking the reason monks have to work harder than nin to keep up the damage. It isn't that we have a harder rotation, it isn't exactly tricky and honestly, no harder than the nin from what I know of nin. It's the stacks. Always the stacks.

Yes, hit the enemy right and they won't ever fall off, nice and simple, but fights where you can just do that are few and far between, and that is the issue. Primals for example, almost every one of them will make a monk lose his stacks, usually more than once, and pb only goes so far. Leviathan for example takes em away every time he dashes. Ifrit when he jumps, likewise garuda and titan.

In coil you will lose stacks in several situations, be it T5's getting conflagged and having to run in case of dread, or T7's shriek/most of T9. T6 and 8 aren't so bad.

Nin doesn't lose chunks of its dps for dealing with such mechanics apart from the downtime that every other class shares too.