Haven't the time to read all the way through 9 pages of this thread, so apologies in advance if anyone has said this before.
Ozzy, although a show cocker, not a WC, has pulled like a train from day one. I resorted to a Halti very early on, and although his neck muscles are incredibly strong and he could still pull without it turning his head, it at least gave me some measure of control as he couldn't pull quite so hard. Most of his walks were off lead, and he too was really good at walking by my side without a lead When he was about 18 months old he was castrated and couldn't be walked off lead for a good few weeks, so I used an extendable lead, still using the Halti as well. This continued until about 8 months ago when I had to start using an ordinary lead as he started to eat other dogs pooh. He had become so used to the extendable, sometimes long and sometime shortened, that it didn't cause too much problem. He is 5 now, and he has begun to walk on a loose lead a lot of the time, until another dog or human comes into view. But I can cope. He can walk very nicely to heel when the mood takes him, and most of the time we have no need to use the Halti any longer. The only time I have to use it now is when I take both Ozzy and our GR pup Jess out together on my own. Then they both pull in different directions! I think that I will have to introduce Jess to a Halti (or some other head collar) before too long as she has started to pull now.
The moral of this long and boring story is: keep at it, take it in stages and it will come, at least to some extent.
Good luck.