Completely different beast. Raspberry pis are full blown computers. Arduinos are microcontrollers with a little supporting circuitry. Even a pi zero beats a standard arduino out of the water.
How often do you need a full OS?
Are you browsing HN with an Arduino?
Are you browsing HN on a pi?
No, of course not.
So thus, neither Arduinos nor Raspberry Pis are things that need to exist.
Uh? All the time??
While the Arduino can replace a Pi in many projects I've seen, if you're reason for dropping th Pi is to avoid the issues corporations bring to the table, you're not going to be any happier with the Arduino.
Do you also compare sandals and shoes, claiming they have the same purpose? Sounds ridiculous? Well...