"I thought if I made a really good engine, making a game would be the easy part!" I had similar thoughts when I was younger. Surely if I just upgrade my tools, the hard part will become the easy part!
Jonathan Blow says making engines is easy, because enginedev only takes a relatively small part of development — the game itself takes way more time and energy.
So his argument is, in the grand scheme of things, the engine is not that much work. (Since you're gonna spend ten years working on the game anyway, of course ;)
Programming an engine requires dedication, but pretty much every other area in gamedev require similar dedication to get to an acceptable result.
Solo? Or part of a team?
For certain personality types I think making an engine can make it very easy to get distracted and wind up in the weeds of something you don't actually need, overoptimizing, fence-painting etc. Using an engine can help with self-discipline and focus on the end rather than the means, although then you need to make sure you don't just wind up with a ton of mostly finished tutorial projects and no game.