The difference between Arduino and Raspberry Pi is already one where the Arduino (at least the basic, most popular(?) model) is just a board supporting a small, highly energy efficient microcontroller that you program in C, while the Raspberry Pi (even the Zero) comparatively uses a ton of power and runs a full Linux distro. That difference is huge, and seems to already be in the two different directions you're postulating.
That said, Arduino (the company) has released more boards with faster, more powerful processors over the years, and I wonder if they'll ever give up the flagship Uno model. I sure hope not, since as bjt2n3904 mentioned, it's a great stepping stone for small, cheap, efficient microcontrollers. It's kind of like learning a programming language and realizing how that knowledge applies to most/all other programming languages, whereas so much of the RPi is abstracted behind Linux.
That said, Arduino (the company) has released more boards with faster, more powerful processors over the years, and I wonder if they'll ever give up the flagship Uno model. I sure hope not, since as bjt2n3904 mentioned, it's a great stepping stone for small, cheap, efficient microcontrollers. It's kind of like learning a programming language and realizing how that knowledge applies to most/all other programming languages, whereas so much of the RPi is abstracted behind Linux.