There's a big difference between breaking changes which resolve real pain points in a language/framework/library, like the break between python 2 and 3 and changes that are just for the fun of it, because someone "felt like it was better". I like to view developing software as an investment. You are spending time and money outright, and there is an implicit cost in foregoing other opportunities when you make a technical choice.

Investing in react-router is like investing in a clown. It's a total toss-up. The maintainers could all move on to whatever other hip lib and finally it will be stable, or you can continue betting large sums of money on what is basically a coin flip every 6 months: Are they going to screw with the library again (yes) and will it cause a bunch of bugs in my program (probably). It's a bad investment, esp if you try to upgrade. The ironic part of this is that honestly I feel like the V1 API is the best out of all of them. If they had just iterated and brought breaking changes that were actually needed instead of just those that they felt might be fun, the project would be much better for it in my opinion.

(I know python <-> react-router comparison is apples to oranges but bear with me)