With Astra and Virgin Orbit on the ropes, at this point is it safe to say that Rocket Lab is on the verge of winning the small launch market? Nobody else seems close to having a viable Electron-class launcher. Firefly Alpha, Terran One, and RS1 might yet pan out but those rockets are a size up, and priced accordingly.
Furthermore, with a rocket like Electron needing 16 launches per year to be profitable, it seems unlikely that any other company is going to step in and try to take Electron's market share. The cost of developing a competitor to Electron is simply too high, the return on investment too low, and just getting to a break-even point seems almost insurmountable. Astra and Virgin Orbit have spent well over a billion dollars developing their rockets, and they aren't even close to being able to successfully launch 16 rockets in a year. Honestly, I think the most probable outcome is that both of those companies will go bankrupt before they manage to launch another 16 rockets, combined. I just can't see how anyone can build a competitor for Electron at this point.
That being said, although Electron's market share seems very safe, it's never going to be particularly profitable, nor is it going to make Rocket Lab into a company worth tens of billions of dollars. Nevertheless, Electron gives Rocket Lab plenty of experience, launch heritage, and industry connections which is invaluable.