You're correct: the proc chance per cast doesn't change when casting indefinitely. But that means you get an increase in PPM as more events occur, all with equal proc chance as previously, within the same time frame.
For example, a 2.5s spell can be cast 4 times in 10 seconds with 0% Haste.
With 25% Haste, that spell becomes a 2.0s cast allowing you to cast it 5 times in those 10 seconds.
In both examples, each individual cast of the arbitrary spell has the same X% chance to proc it, except in the hasted scenario you have an additional event that triggers it in the same time frame. That's a direct increase to PPM.
Now consider when you aren't casting indefinitely within a time frame: the haste factor in the equation allows the hasted scenario to retain the same PPM without it being wasted just because there was nothing to heal for example. It normalizes it. In fact, without the haste in the equation, Haste rating from gear would actually cancel out the effects of RPPM.Second, people with Windsong reach PPMs of 4-5 (or more) per stat with nowhere near 50% haste: haste scales the proc rate much faster than any of the described formulas.
Because it's probably bugged.
Thank you for this. For some reason I forgot that , with more haste, you end up having more casts in a given time frame which you need to multiply with the proc %.
The entire RPPM mechanics must be bugged: then, or everything has a much higher RPPM than stated. I'm not complaining!