Summary of JA vs Magic Procs using simple maths and assuming a 20% JA proc rate and 5% magic proc rate (best estimates based on available data). This assumes perfect use every cooldown, Dia is mostly limited by magic delay and casting time outside of human error:
7 Chances for Steps + Flourishes every 60 seconds
20 Chances for Dia every 60 seconds
Over a 60 second period, there is a 20% chance 4 times, every 15 seconds, for Steps to proc, and over a 60 second period, there is a 20% chance 3 times, every 20 seconds, for Flourishes to proc for a combined
total of a 20% chance 7 times over a period of 60 seconds for JAs to proc.
Over a 60 second period, there is a 5% chance 20 times, every 3 seconds, for Dia to proc.
JAs: 1-(0.8^7) = 20.97% chance of nonoccurrence, or a 79.03% chance of occurrence
Dia: 1-(0.95^20)= 35.85% chance of nonoccurrence, or a 64.15% chance of occurrence
4 Chances for Steps + Flourishes over 40 seconds
14 Chances for Dia over 42 seconds
JAs: 1-(0.8^4) = 40.96% chance of nonoccurrence, or 59.04% chance of occurrence.
Dia: 1-(0.95^14) = 48.77% chance of nonoccurrence, or 51.23% chance of occurrence.
4 Chances for Steps + Flourishes over 20 seconds
7 Chances for Dia over 21 seconds
JAs: 1-(0.8^4) = 40.96% chance of nonoccurrence, or 59.04% chance of occurrence.
Dia: 1-(0.95^7) = 69.83% chance of nonoccurrence, or 30.17% chance of occurrence.
So in a scenario where you're starting a fight with both JAs available off the get-go, magic procs are waaaay behind over a similar amount of elapsed time. If you for some reason have both at max recast, the gap is smaller. That's an unreasonable scenario, however, unless dealing with links.
Seems like average currency pull for the veteran THF/DNC is around 350-450 singles. Unfortunately, I haven't heard of any other class coming close.
I do this easily on my BLU/DNC, 350 being a very low average and something I wouldn't even include in my range. 390~460 is closer to what I pull daily, it's hard to go any lower (current record is 487, could pull higher but it seems everyone on Valefor does Dyna during the hours that I can play). My RDM/DNC mule gets much lower though, 320~390.