Adam
I feel that there's no such thing as a poor cleaning system. But any system can be executed poorly, or used in an inappropriate situation.
I'll give you a personal example. Last year, Masonic Lodge, an 80+ year old black and white chequered carpet. No underlay, nailed to the floor. Pile lifted 4 times. treated candle wax with iron and paper, during which soil was wicking up from beneath. Any water system could have created major wicking problems. I used Host Dry Extraction. It wasn't the best clean in the world, but it was the appropriate system to use, and it was 100% safe. We often come across problem cases whereby system X, Y or Z will perform better than A, B or C even though they may not remove as much soil. That's why we're called professionals, because we can apply our knowledge and skills to challenging situations.
Safe and happy cleaning
Ken