You can use either watts or amps, but either way, you will have to convert when comparing PWM with MPPT. So, convert PWM output to watts, or MPPT output to amps, but one or the other has to be done, and it makes little difference as to which. I chose to use watts, since it's easier.
Yes, I redid the math slightly before seeing your post - the curves tend to be flat @Isc until you get to around 15V. So, I was underestimating the PWM output. But, I was also trying to be conservative in the calculations.
But no, you don't get nearly the same amps (as averaged by the PWM duty cycle) until near the end with PWM - that's why you have a controller in the first place. Bulk charging at full current ends long before the battery is fully charged. That's when the controller goes into constant voltage (absorption) mode. Once it goes into constant voltage charging, there's an excess of solar power available, so PWM or MPPT doesn't matter.
