Call it what you will - a 'stim', 'buzz' ' tap' - whatever. It hurts. It wouldn't be effective if it didn't. It's designed to hurt.
If it is solely designed to hurt, why are the low levels painless? E-collars can be used incredibly subtly. If you don't know that a stim can be painless, you shouldn't really be opining on e-collars.
There are better ways. Often they take longer, take more commitment and more dedication but they exisit.
Honestly, I am not sure that they do. There is £50k on the table for any +R trainer who can take a dog who has killed stock and make it safe. Simone Mueller, of Predation Substitute Training, has said it probably can't be done.
There's also the issue, when training takes a long time, of the restriction placed on the dog and the rest of the household during that time. It's a matter of balancing the loss of welfare caused by the restriction (for the rest of the household, not just the dog) and the loss of welfare caused by punishment. I think about that quite hard, because I don't want to be unfair to my dogs.
And management DOES sometimes fail, which is why getting the dog to understand what you want quickly can be important.
And @twistyizzy you are obviously a highly skilled and very organised dog trainer (and I'm not being snarky). I can walk my dogs, both together, off-lead, within feet of sheep, off-lead (which I only do with the owner's permission), but I'll be honest: it took me moderate aversion to get them there.