I would say that most springer fans over the age of about 35 will be well aware of Mr Cardew's workings, much of which was very eye-opening at the time.
And his books, The Airgun from trigger to muzzle and, later, The Airgun from trigger to target, can be considered "must haves" for many wanting to work on their own guns.
However, time stands still for no man and although his work was invaluable to us, modern knowledge and thinking has moved on, with the likes of Jim Tyler and Dr Mike taking things so much further and actually dispelling some of GC's findings. Like the dependance of the springer on combustion to make decent power. And we have more than our fair share of very knowledgeable tuners right here on the BBS.
Taking nothing away from the great man, though....his works can be regarded as pioneering and probably helped pave the way for the modern tuner.