To be fair, we didn't drop everything and do a rewrite. Over the last 3.5 years (the length of time for this project), our total engineering team has ranged from 50-90 people. For the first year it was me and two other people. Then for the 2 years following that it was 9 people total.
It wasn't until late last year that we made the decision to go all in on the rewrite and made that the focus of everyone in engineering. And we did that because we had 4 years of experience trying to get v2 and Flux to be successful, with modest results.
Most of the time we were developing this version, we were spending massively more engineering effort on developing v2 or maintaining v1 for our customers.