I’ve actually never used Arduino so far. And mostly for the same reason you hesitated as well. Many people I talked to believe that Arduino is bad, because it hides so much from the user. So, people never learn the hard/real way of doing things. But, as you said, I think there is a lot of value in Arduino.
I’ve done a couple projects with Raspberry Pi 3, but I’m also not an expert with python. I think you are right that Arduino is best for sensor stuff, when you need to access a lot of hardware. Raspberry Pi is (probably) really good for AI and TCP/IP stuff or very big complicated projects.
I’ve recently read an article about people who tried to use Arduino in a real product (was for a kickstarter). I think the costs are a big problem. There’s probably quite much markup on Arduino’s so you won’t be very competitive with your product, if you try to sell in large quantities. Especially if it’s a consumer customer. But, I think it’s perfectly ok for industrial customers and also research.
Raspberry Pi also has industrial versions, with almost all I/Os exposed via an industrial interface.
I mean Raspberry Pi in general was a huge change for the whole market. It was the start of a new era. A computer that fits on the palm of your hand. It think it also played a huge part in shaping the maker community. It’s incredible what Makers create in their own free-time.