As with all things, a balance is often the best long term strategy. If one uses the strategy of using the best tool for the job, if that job is for building an application that will run in the front office of SMB on office worker computers, I am probably best building a Microsoft-only application tightly integrated with the OS and the Microsoft Office Suite. And, just as valid, if I am building a back office accounting program that I want to be able to sell to any business, I should probably think about a cross-platform multi-tiered approach that supports plug-and-play of different databases, like MySQL and MS SQL.
HOWEVER

(you knew that was coming)
I have made a living as a generalist, a jack-of-all-trades, that has allowed me to often see the bigger picture and shift the focus of a team to a more successful path and outcome. And I enjoy doing that. This also allows me the luxury (yes, I would classify it as such) to work with multiple tools, using multiple languages and languages, on multiple operating systems. And there are plenty of career paths that one can take with such a strategy.
But I also recognize that each of those successful projects also required the teamwork of specialists. Those people give up the luxury of heterogeneous environments and choose to take on tunnel vision, actively blocking out other things, in order to learn something to a far deeper degree of understanding. The benefit of this path is the ability to create a finely tuned, esthetically pleasing, high-performing, eminently functional piece of technology/art that all McGuyvers will admire more than most people who don't understand the discipline required of a specialist.
The truly talented individuals (who I aspire to be) have that ever elusive ability to be McGuyvers that take expeditions down specialist paths, create great works, and learn new things, and then seamlessly return to the McGyver way and catch back up quickly to allow another expedition. I honestly worship these people and all they accomplish.