Often, when people who are against force free training speak out about it they bring up several occasions where force free didn’t work for a dog they knew of. It’s not that the application of the training failed, it’s the style of training that failed. Similarly, if someone who uses punishment applies it seemingly “incorrectly” and it doesn’t work for the dog, it’s the application that failed and not the style of training.
There are always going to be potential issues with the application of training, with reinforcement timing, motivators, timing of distance and distractions, etc, that’s a lot of variables! That said, just because there is a potential flaw in the application of working with one dog doesn’t mean the entire style of training should be dismissed as non-functional.