Pebble never said that anyone "needs" to buy the ring sizing kit. They did suggest that you buy the sizing kit from them for $10, OR 3D print it at home, OR visit a jeweler.

The ring has a button on it that you are going to press often, and you will likely wear it on a different finger than you would normally wear a ring on. That is/was the advantage of the sizing kit IMO: you can try the different sizes and wear the "dummy" ring for a couple of hours or a day and get a better idea of what size and finger will work best for you.

I think calling the ring sizing a "debacle" is being a little over-dramatic. It is a shame the ring kit is off on sizing, but how big of a problem it is, is kind of an unknown right now. It's a limited production product, there will be problems at the start, just like there have been with the Pebble Time 2.