I am a professional dog trainer.
I am of course generalising, as there are always going to be exceptions, but as many have said upthread, the majority of dogs that are of concern to the general public are very unlikely to have owners who are paying for and dedicated to ongoing training and responsible dog ownership.
(btw - I do not agree with the XL bully ban because I believe it will be ineffective. However, I do believe we need some form of far stricter regulation around ownership of large powerful breeds. I have seen some examples of outstanding XL bullies with wonderful owners, but being completely honest these are few and far between. I have observed many more examples of people that are in no way equipped to own or handle XL bullies or other similarly powerful/high drive/guarding breeds for that matter)
Separately, is regulating training a good idea? Potentially at a high level in terms of do you have adequate insurance, risk management etc. However dog training is so nuanced, and there are so many different approaches, I can't see that it would be in any way feasible that actual training techniques could be mandated or regulated in any sort of detail.
Some of the best dog trainers who compete at a high level (Robert Cabral, Ivan Balabanov being a couple I can think of off the top of my head who have social media "profile") are balanced (i.e. use aversives in their training). Whether you would choose to use the same methods or not is up to you, but are we honestly saying that someone who competes in competitive sports such as IPO or Schutzhund to the highest level in the world would not be fit to train a pet labradoodle?
Conversely, some of the high profile positive only trainers (Zak George and Victoria Stillwell are two that spring to mind) are in my opinion utterly useless. I wouldn't let them go near my dog with a barge pole, let alone trust them to train a truly aggressive powerful high drive breed.
There are of course extremely skilled positive only trainers, and utterly terrible balanced trainers as well.
The biggest difference is often in the skill of the trainer, not necessarily the blanket training techniques being applied, and I have no idea how a government/local authority that has already demonstrated a real lack of knowledge in this space could even begin to make a considered judgement on how a trainer would "make the grade".