Today the same amount of knowledge makes you barely passable in a single niche domain. Consider web development. To get really good at modern web development, you need to know modern javascript, CSS and html. You need to understand how browsers work and all the quirks of how http requests and loads webpages - including what dozens of http headers do and how they interact. You need to understand the browser rendering process, performance tools, accessibility and debugging tools. And learn dozens of javascript libraries, like react, express, webpack, database wrappers, and so on. It’s accomplishment to learn all of that. But if you do, you still only know web programming. That knowledge doesn’t really translate to operating systems work, mobile development, databases, AI, embedded, etc.
Most professional programmers only have the inclination and capacity to learn one ecosystem. And, even then usually with big holes in their knowledge. True polyglots are rare because the mountain you need to climb to get there is higher. But we also depend on polyglots to guide us toward useful tools. Language / ecosystem choice still matters. It matters for performance, velocity, security and compatibility. But how can you really evaluate that stuff unless you’ve spent time debugging Go programs, or tried to squeeze every last drop of performance out of a big legacy Java monolith?
We’re left talking imperfectly from our own experiences. And living in whichever niche of programming we’ve carved out for ourselves. The days of everyone being all terrain programmers is over.