Incoming wall of text. Sorry.
A few years ago when I could foresee myself having some time on my hands

, I did weigh up Ardruino vs. going somewhat deeper into rolling custom boards with more exotic, specific micros.
I had a bucket list(!) of home projects and after considering each one, realized that the Ardrino family satisfied the needs mostly, the big lure was the fact that if I run a standard board across all projects, I could cannibalize, at a pinch, if things failed.
And the mature programming interface. I knew that what ever Linux I happened to be on, I could plug in the board and have it connect. As a novice lacking only in experience, quick research indicated that the big micro suppliers would fall short for rapid application development, due to the complexity and inconsistency.
Coming out the other side, the only thing I'm dirty about is that we didn't have this fancy stuff when I was a little bloke. However, where I feel the need to speak up in these discussions is I still haven't found a reason, except for hardware limitation, why any of the Pro eco-systems are worth bothering with.
Any of the big chip makers could have owned the Arduino market. Yet, silly marketing wank and competitiveness has prevented them still from lowering themselves to create a simple, compelling turn-key solution to attract an audience who might like to get into mircos which might actually be greater than the existing number of rusted-on users, I'd wager.
What do you think?