I agree. Getting competent in another language/framework isn't difficult -- I've done it more times than I can count. I agree having a few different perspectives is good; learn a functional language, learn assembly, etc.
I'm not dismissing problem solving, organization, logic, etc. But you can't dismiss the practical details like what APIs exist, what bugs they have, how do you call them, language features, platform differences, XML configuration file of the week, etc. You can only hold so much of that in your mind at once. And having that is what gives you productivity.
I agree with you and I'm not dismissing. Each stack has its own share of problems and intricacies, but some are more complicated (.NET, JVM languages). Speaking from my own experience, building Java/.NET inter-operable web services having involved WS-Security extensions (STS, SAML assertion) wasn't quite pleasant.
Other stacks follow different programming schools of thought and may result in different approach to a problem.
I'm a firm believer in using the right technology for the problem rather than simply the technology that you know best. I'm actually hoping that .Net becomes more appropriate for more tasks (especially on Linux) but for now that's not the case.
But the point is that having a bunch of radically different technologies for every task is far from optimal. You simply can't master them all. Right now I made a bunch of technology purchases and I'm looking at Unity development, Tizen development, and Android development all at the same time along with the usual day to day .net stuff and it's way too much. Having a single language/framework would make it a lot easier to produce a result.
I'm not dismissing problem solving, organization, logic, etc. But you can't dismiss the practical details like what APIs exist, what bugs they have, how do you call them, language features, platform differences, XML configuration file of the week, etc. You can only hold so much of that in your mind at once. And having that is what gives you productivity.