When the NHS was set up, it was intended to deal with broken bones, loss of limbs, diseases, maternity care and the like. Expensive procedures such as open heart surgery did not exist and many issues such as mental health and cancer were not recognised as being treatable.
All of these now form part of the NHS remit, along with cosmetic surgery, drug treatments, gender issues and other 'self inflicted' conditions. To paraphrase, they don't just need a chisel and a screwdriver, they need a whole range of tools.
Since the formation of the NHS, the population has grown by around 40%, in part though immigration and in part through improved infant mortality and an aging population. Many who 70 years ago would not have survived, now do so as a result of improved health care. Currently something like 10% of the population have regular need of NHS care.
Part the problem is the NHS is mainly reactive. Until a patient walks (or is carried) through the door, they don't know what resources they will need, so they have personnel on standby, operating theatres kept in a state of readiness etc. They are creating more preventative processes to encourage people to stop smoking, drinking, take their medicine, etc but these take time to show benefits and unfortunately there are a lot of people who don't see it as their personal responsibility to look after themselves.
I do believe there is a lot of waste in the NHS - IT systems that don't do as required - on a small scale how often do we see medical personnel on this forum asking about how to create a system to manage a surgeon or consultants time? I've been involved with developing an access application to manage the distribution of drugs and medical equipment as the multi million pound corporate systems could not cope with rapid change. 20 years ago Labour created the public/private partnership which became a license for the private element to print money. Something I don't think can be resolved until (I think) 2030. You have doctors and surgeons who have excellent skills for their profession but they don't necessarily have the skills for managing a large organisation. Similarly you can have professional managers and administrators who do not understand the intricacies of the medical profession.
Overall, my experiences with the NHS have been positive so I don't have an axe to grind but I do think the way the NHS is organised and funded needs a complete overhaul.