At this point it's getting hard to start from scratch and get to feature parity alone.

There are people that still do or try it but you certainly lose nothing by exploring if forking an existing client would work, too. After all you learn a thing or two by looking into existing projects.

In my experience, those who started their own clients are often very opinionated and not too welcoming of big new features or changes to their existing features, making it hard to have improvements flow both way.

I think, at some point some client will manage to get ahead of others and this will get more contributors to join forces, further getting it ahead. But not yet as somehow devs still think they can single-handedly catch up and do a better job.