I have a day job. Right now, I do open source purely on the side, but if I was to get enough donations/sponsors or I got paid for doing open source work, I’d happily start doing it full-time. I do sometimes contribute to open source during my paid work, but that’s more an exception than a rule.
There are different variations of depressions. In particular, it differs between acute and chronic occurrence.
As far as I know, acute occurrences tend to be more intense (as experienced and reported in standardised tests) on average than chronic ones. Here, the risk of, e.g. suicide is also highest. However, long-term depression has a much more long-lasting impact on one's life, so I don't want to downplay it in any way.
Acute episodes tend to have a duration of only a few weeks or months so short-term therapy can be of great help here.
I agree that chronic depression requires long-term support. Your analogy with insulin and diabetes is excellent. And yes, the NHS falls short in this area, unfortunately. It would be great if more people could get the care they need and I hope it will become possible.
So yes, the NHS is not without its flaws. But considering the little funding it receives, it provides excellent care. It just shouldn't be so underfunded. I also think that it is also remarkably well-organised compared to other countries, e.g. Germany, where everything is much more bureaucratic and expensive. I also think it's significantly that countries with more privatised health care like the US.
The NHS also offers a range of other talking therapies /counselling, e.g. counselling for depression. The waiting times here can be shorter than for CBT.
If you're in dire need for help (depends on your scores and initial phone interview), you will be seen or referred quickly (within less than a month).
Any GP will refer you. If you need help with your mental health, just ask your GP for a referral, fill out the form and you will get help. It's a great system. (Did I mention that this doesn't cost anything?)
For long-term psychotherapy, you need to go private, but in many cases, a short-term intervention (e.g. over 12 weeks) is sufficient to get you through the worst and on the right track.