This is a very interesting subject and i think there are pros and cons with both options of training, here or abroad. Firstly i think you have a very valid point on the "Zero to Hero" courses. These should be sold as an introductory courses and no way will someone who has never even handled a wing before attend one of these and expect to come home after about 10 days ready to fly off on their own. But the story is different for everyone and for some, these courses abroad will be the perfect way to progress in the sport. I think training in the uk will actually put lots of people off the sport to be honest.
I started my training with you way back, probably in about 2012, i forget now, but i was really excited about it then. I paid in full up front and then waited for the weather to play ball. To cut a long story short i came up to membury a few times (about 200 miles), slept in the van and played the normal uk game of waiting for the correct conditions to learn. On my first attempt to take off i cocked up which resulted in me striking the prop on the floor! That cost me another few hundred quid to pay for that. In the end i got fed up with trying to match up days off with a 200 mile trip and then hoping that the weather would be ok. So in short i paid for a full course had a couple of days ground training, one failed take off and then i gave up. I then didnt bother to try again until a few years later thinking that it was never going to happen.
In 2018 i got the interest (and time) to give it another go. This time luck was on my side and i did a weeks training in Mere uk. The weather was amazing and spent hours in the field honing my ground handling skills. ( i already had quite a bit of ground handling under my belt) This week ended in a couple of great flights. I then booked my second week with the same company in italy. Again luck was on my side in italy and the weather was flyable (variable) everyday. This meant we were in the air every morning by about 8am doing exercises and again every evening when it cooled off again. We did low passes, dead engine spot landings cross country flights etc etc all in a week! This gave me much more experience than i would of crammed in in the uk.
All that said when i got home it was still another story. Flying for the first time without an instructor keeping an eye on you was daunting but because i had done quite a bit of flying on my course i eventually went for it and ive not looked back. I did way more flying in that one week in italy than ive managed to get in here in the last 6 months.
So i think there is a place for both options. If i had not taken the route of going to italy i would still not be flying thats for sure. I agree that in most cases further training will be needed when you get back to this country. I also agree with you that learning in the country you are going to fly in is also a good idea.
I think anyone who is considering going to do a course in spain or similar should like you say simon take it as an introduction into the sport and expect to have to spend a few quid with you when they get back to further their skills. But if we discourage them from going in the first place they may never take up the sport.
Only my opinion!