I think from the perspective of a developer with less than 3 years of experience, what you're saying makes sense. But there are developers with 10 or 15 years of experience and they've had plenty of time to become good at both. Also many junior devs will become senior over the next few years and they shouldn't limit themselves to just front end or back end. It limits your potential and future options. Anyway that's why I used those harsh words. Your article makes sense from one perspective but I don't think it's productive to limit one's self.

I don't buy arguments about complexity becoming too much. A lot of complexity we see today is unnecessary complexity and of course it is challenging to manage a lot of complexity but the divide between front end and back end isn't the main factor which makes software development challenging.

You CAN learn it all to a very high standard if you have the will and only when you have a solid understanding of both front end and back end you start to notice unnecessary complexity and learn to avoid it.