Earlier quoted context omitted.
I had a very similar experience as you. But I think you're being too humble. Whether you wrote 15 applications or just one or two, does that really matter? Designing, exploring, writing, iterating on and maintaining these applications _for years_ have given you insights, battle scars and tacit knowledge that can only be gained through experience and continuous learning. Not to mention the different environments techn…
Yeah I don't deny I'm a far better programmer now than 10 years ago, and may even be better than the average in some respect, but most of it is as you say tacit knowledge. I don't have any catchy slogans or rules to teach. I also understand that there is so much I don't know. Even if I hone my skills until the day I die, I'll never be so certain I know the best approach as I was when I was younger.
There is the work you do for money for food and rent, but there is also the work you do for yourself to improve your own craft. Often on the same project.
I think you’re describing the disappointing but grounding perspective gained as one gets older and wiser.