The result is that now, all users of either of these extensions benefit from a better and faster product, thanks to emulation between competing projects. This would not necessarily happen in the absence of competition. In the end, users benefit.
(Disclaimer: I am one of the authors of the performance study)
[1]: https://whotracks.me/blog/adblockers_performance_study.html
If for whatever reason uBlock Origin went away tomorrow there would be a fork. uBlock Origin is the second (or third, I forget) fork of the original project.
Sure, no argument there. But the original comment said that in this case it is "much needed", suggesting something more specific than just "competition is generally good".
Lots of comments here are making non-specific arguments that "competition" leads directly to improvements in products/technology. It seems to me what is missing here is a concrete idea for making an ad-blocker work better, not an avenue for making a new/different approach available. (In particular, the goals of this project seem to be much more about working around upcoming Chrome extension changes rather than about improving the behavior in some way)