So, are you spamming your main button or trying to hit it in a certain rhythm as alluded to by the OP?
I am a spammer. If I had rhythm with my hands, I would have been able to play an instrument instead of just sing, hehe. But, people do tend to spam in a certain interval. It isn't too difficult to create the /click macros, put a copy of your spells up on an inactive bar and spam away at a targetting dummy. This way you can see X goes off right but Y is not getting hit soon enough and Z is causing my macro to stall and add or remove nulls accordingly.

You could do: /castsequence Moonfire, Insect Swarm, Wrath, Wrath, Wrath, Warth, Moonfire, Wrath, Wrath, Insect Swarm, Wrath, Wrath
Except not. This doesn't account for things like Nature's Grace, which hastes your next spell after a crit, or other haste procs which is why castsequence doesn't work as a spam button for certain classes. However, using /click covers that by allowing you to put things that never change {cooldowns} on a certain priority via the null macros and things that don't have cooldowns or timable uses {wrath, starfire} into a castrandom to be used to fill in the "idle" time.