The importance of I/O pin DC current
The simple answer is: It doesn't matter.

Both Arduino and the Raspberry Pi, and every other common microcontroller board, are designed to control things, not provide power to things.

Digital IO pins aren't designed to drive heavy loads. Yes, some (like the Arduino) can provide slightly more current, but that is really unimportant for most projects.

Yes, some boards have more powerful power supply circuits on them so you can draw more current from their power supplies, but again that is largely irrelevant.

The one thing that you seem to be forgetting (or haven't realised) is that the microcontroller board does not have to supply all the power.

The Arduino, Pi, Teensy, chipKIT, whatever, is merely a controller. If your system needs more current it is up to you to provide that current. The Arduino etc merely controls the circuit or device that it is connected to.

It is very common to have multiple power supplies in a large project - each providing different voltages, or being used for different specific tasks within the project.

Just one thing you need to remember: Connect the grounds.