You cant just keep telling people a horse and buggy is good enough soon the cars will run you off the road.
That's where the analogy is flawed IMHO.
We have tens of thousands of people who know how to use this "horse and buggy", as you call it. Thousands of libraries, many add-on products (shields, etc.). To do something as simple as switching a processor (as they did with the Leondardo) invalidates some of that.
I do think if the product needs reform to stay current ...
But what do you mean by that? For years I used Microsoft products and just when I had learned how to use (say) one of their database libraries, they "improved" it, throwing all that knowledge out the window.
To monitor water-tank levels, turn on lights at night, operate key-pad doors, feed the fish, water the garden, do many of the things that the Arduino does well these days, just doesn't need more power.