Frankly, if React didn’t exist, and assuming none of the other post React frameworks ever came to exist, we would likely have a duopoly of Angular and EmberJS. I personally do not like Angular at all, but EmberJS was awesome. It’s performance was slightly sluggish but nothing having more developers due to higher popularity couldn’t have solved.
If I had to be absolutely honest, the developer experience side of EmberJS was miles ahead of what React is today. NextJS is only just coming closer but I’m not even sure it’s there yet.
If React hadn’t existed, and more people had experienced EmberJS, I think web development would have been a far better experience today than it is right now.