Mellow Yellow isn't the strongest of wheel cleaners but is still good at it's job.
I'm afraid you have just been using it incorrectly, if you spray on all the wheels it will dry out before you get round them all, it's just not designed to be used this way. If you just go a wheel at a time it should work much better.
Wolf's Brake Duster is the complete opposite, this is designed to be sprayed on and left for a while, it is suppose to completely dry on the wheel (some people have left it on overnight!). Then when you go round with the pressure washer, it peels off the brake dust. This still can be agitated for really bad alloys. Don't forget, you can also use Wolf's Brake Duster (now called deironiser) on your paintwork to get rid of any iron particles, works very similar to Iron X but just a little slower.
As Jimble has posted below, ValetPro Bilberry is a good wheel cleaner and normally my go to wheel cleaner, I love it through a foaming spray head.