He's 100% correct. Learning new languages/frameworks/tools is fun and can be useful if you have projects that can make use of them. But they don't contribute to

He's 100% correct. Learning new languages/frameworks/tools is fun and can be useful if you have projects that can make use of them. But they don't contribute to making you a "better developer" very much after a point. There's diminishing returns on learning new languages. So, once you've learned a dozen, then learning the thirteenth or the twentieth will not contribute greatly to your overall developer skills. Creating a new project unlike any you've done in the past will do more to contribute to your skills as a developer, whether that project is in a new language or one you already know, than just picking up a new language and making your 10th simple blog.