I find your results curious, since I get great results with bonnet cleaning.
Tip 1: You probably can't use bonnet cleaning in the same way as extraction cleaning, one pass with no manual work, etc. I find that I have to pretreat and -hand scrub- most trouble spots in a room before I run the bonnet machine. It adds five to ten minutes per room if the rooms are spotty.
Tip 2: The cotton pads are essential. Dirt just doesn't stick to the synthetic pads in my experience.
The synthetic pads loosen, but do not remove. I have to follow the fully synthetic pads or scrubber pads with cotton, or at least a cotton blend.
Tip 3: I make a green cocktail mixing Encap Green with a dash of vacaway's Spot-and-Boost Green. I always use 6-8oz per gallon.
Tip 4: Sometimes you have to dwell in the really dirty area with the bonnet machine for a little bit.
Using this method, the only time I have trouble is with urine, red wine, and brightly colored food spills, or gum/tar like substances. But then doesn't eveybody have trouble with those? I have been doing this full time for three years and 85% of my customers are thrilled, 12% are just OK with it and 3% didn't like the job. Stairs (always the dirtiest carpets) get a "wow" reaction 99% of the time.
I DO in fact get some tip bloom on the dirtiest carpets that I treat aggressively. I also get a fair amount of loose fuzz on freize carpets in places that have not had traffic. On the whole, those carpets are much better off being cleaned with my agressive method. These carpets are badly worn anyways. The alternative for many of the carpets that I clean would be REPLACEMENT. So instead the customer gets a partially tip-bloomed carpet that's good for another year or two. They don't know what tip bloom is. Maybe the IICRC would give me a failing grade, but the customers don't.
Many cleaners (and male workers in general) have an almost religious belief against doing anything by hand, without some power tool involved. "I must do it with a machine!" I get appalled reactions from male customers too, "Why would you do anything without a power tool?!" For me, the manual work makes the whole service work, doing what the machines can't do.