There's your lighting line, right there: "Overall my takeaway is that my games, especially my larger ones, should rely less on planning and make more room for testing."
It's so, so easy to get carried away typing away in a document about the perfect game in your head. And, like you said, it's easy to think you know that, without actually knowing it, until you've put in the practice.
I'm guilty of docubating, myself. I think I put off the making, and the subsequent testing, because seeing my perfect concept become imperfect reality stings a lot.
But it's important to press on, because the sting means that the medicine is working.