I run all my off road runs in Adidas Swoops which have very little cushioning and during these hot months the ground can be very hard as well, like you I am on the heavier side at just over 16st. As most of my running is now off road, when I switch back to my road shoes (NB 751) I notice quite a difference in the heel height and am thinking of changing them for lighter shoes, how light depends on how brave I am in the shop!
My point is I changed my NB854 (never really liked them) for the NB751 and thought they were brilliant, now after a lot of running in the Swoops I'm not so keen on them. Which leads me to believe it really is a case of conditioning yourself to less cushioned shoes which can take some time.
Incidentally I did cut my Achilles heel tabs out of the Swoops and was amazed at the difference it made to the soreness of my Achilles after runs. Like you I was a bit sceptical at ruining a good pair of shoes, but I’d had them for a while and went for it. I didn't just hack them off but cut along the seem, cut out the stuffing and folded any excess material back into the seem and sewed back up, I did rather a good job even though I say so myself - unfortunately I now can't get the wife to sew anything for me anymore!
A lot has been said on the forums with regard to forefoot striking/Pirie/Pose, and that this is the "correct" technique to adopt when running, I happen to agree with these principles. But I am very cautious about telling someone they should change their style because it is "wrong" if they don't have any problems and are very happy with what they are achieving in the sport, whether it be recreational or competition.
Like you I also think that if you are stuck in a continued cycle of injury then you need to do something to get out of it. This will require a change of some description, such as technique (or strength, or flexibility).
I know prevention is better than cure, but quite a lot of people run less than 15 miles per week injury free because they don't do the very high mileage to over stress their weaknesses - why change. I think people should have a better understanding of the facts though.
I should have added that I don't agree with your physio about not being able to build up the strenght required. This process should be done gradually and it can take some people longer than others but that statement is wrong. That's like saying don't take up archery (or any other sport) you're not strong enough and can never be...
My view is that all intrinsic injuries result because of a lack of strength somewhere in the chain, regardless of what technique you adopt or what biomechanical inefficiencies you may have. With poor technique or biomechanical inefficiencies you would require more strength to avoid injury than someone without these issues.
Certain techniques cause greater stress in different parts of the body, where the weak link lies is different for all of us. Many people take up running after years of inactivity or (like me) probably carry too much weight and therefore don't have the developed strength to avoid injury. I would always suggest some sort of strength program to complement your running as an aid to avoiding injury.
All top athletes are very strong, far more so than some of their physiques would suggest. I guess what your physio is suggesting by 'initially causing more problems than it will solve' is that you need to build new strength in diferent areas to cope with the new technique.
For the record I agree with the principals that Pirie put forward in his book, though I also would go along with the principal 'if it ain't broke don't fix it'. The first objective is to enjoy your running for some people that is just getting out there and doing it, and for others it is improvement and competition or a blend of both!