The Raspberry Pi Pico is completely different to the previous generations of Raspberry Pi computers. The main difference between a Raspberry Pi 5 and a Raspberry Pi Pico is that they are two completely different classes of devices designed for totally different purposes.
This aligns with comparisons showing the Pi 5 is dramatically faster (36× CPU speed), has gigabytes of RAM, and supports 64‑bit computing, while the Pico is tiny and optimized for embedded tasks.