You shouldn't conflate those two, as they're very different things. TMS is currently undergoing lots of trials.

ECT does have significant negative side effects, but it does seem to help some people. You may be right that it wouldn't be approved as a new treatment today.

Just a word of caution, keep in mind that all those trials are designed around very crude observation or short term duration. Also, lot of things are going into trial that shouldn't.

That being said I do have an uncle with Parkison who had a neurostimulator implanted (DBS) 15 years ago. It worked quite well for a while, more than any medication at the time. It doesn't anymore, and he has lost cognitive abilities also, which is most likely due to the progressive nature of the disease, rather than DBS. This technique has been in clinical trial for 20+ years...

Side note regarding DBS: There's some interesting research in grafting a nerve (I could be misremembering, but it's definitely a nerve graft) onto the substantia nigra (a part of the brain that we know produces dopamine), and then doing DBS on that region. Early stages, phase I trial, but a neat idea nonetheless.

ECT would be approved today. It is a valuable tool in the last line treatment of otherwise intractable depression.