The "fully trained" wording is curious since AFAIK the standard for a service animal is that it be trained to perform a specific task for the owner (maybe turn on a light switch or alert when blood sugar is a problem) with no requirement of any further training. A dog could be feral or very badly behaved and if it is trained for just one task, no matter how minor, it's a service animal and no one is allowed to question its training.

The OP seems to suggest that DOT has no problem with DL banning pit bulls (and maybe other breeds) as ESAs, just not as genuine service dogs.