I've used Nova for years as a solid base for Zooper on past phones and KLWP on my 6P. However, I'm going with the default launcher this time. A big part of the Pixel sell for me was all the talk about a buttery-smooth user experience and I'm guessing the launcher is going to be a big contributor to that experience. If I want more customization, I may start tinkering with Nova and KLWP again.
That all said, I can see the car analogy. Custom "themes" are like modded cars. For every well-done, tastefully modded car you see, you'll have seen a dozen riced-out Civics that make a bunch of noise and have a bunch of cheesy aftermarket parts slapped on them. I can verify - my phone is like one of those Civics