I definitely recommend every WordPress developer step out and learn other technologies. Get familiar with other programming languages, cloud services such as AWS, etc. It will make you a better WordPress developer and it's good to get outside of the "echo chamber" that is the WordPress community.

That being said, WordPress isn't the end all be all. But it is definitely good for a wide variety of things. But I wouldn't necessarily say build every type of application on top of it.

From a product development standpoint the biggest strengths is it's ecosystem and the size of it's user base. Even if your product is a SaaS service that is platform agnostic, providing a WordPress plugin and marketing to the WordPress community gives you a very large targeted audience to go after. Much easier than just targeting everyone.

But definitely get out of the WordPress bubble on a regular basis. You'll be a better developer by doing so. The WordPress way of doing something is most definitely NOT always the only way OR the right way to do something.