A good place to start a comparison is when using Vue.js in production looked viable - the October 2015 V1.0 release. At that point Angular has amassed 46k github stars, React had 35k.

Star counts don't tell us everything but they're an OK heuristic of how many people are invested in a library at a point in time. Had Vue.js been in anyway meh it wouldn't have made such a dent in people's attention.

Timing luck, insofar as it exists, is probably weighted towards arriving later. Vue had a chance to listen to the market and solve some of the headaches that developers were voicing about incumbents. V2.0 is basically the best bits of Angular and React.

Again, lots of lessons for product creators.