I feel like the raspberry pi pico is more of a competitor to the arduino than the raspberry pi - there's quite a few applications where having a whole linux operating system is a hindrance compared to running on bare metal, especially anything that needs real time control of signals. (Although you can get around this on the pi by connecting peripherals via USB/serial/i2c which themselves might use MCUs).

Then again, one of the more accessible (IMO) ways of using pi picos is with the arduino environment, or its cousin platformio. I do think that even if in some ways the arduino abstractions can be limiting in some ways, in practice it's often a big timesaver for more casual (and not so casual) applications. It gives you easy access to a large ecosystem of libraries across a lot of hardware platforms.