You can downclock the Pico as you can overclock it in order to reduce power usage. By default AFAIK it already more or less matches the ESP32 power usage, and downclocking it should be able to reach the one of the ESP8266, likely, but I'm not sure.

The RP2040 doesn't have a good low power sleep mode. It uses several hundred uA in sleep and dormant mode versus the ESP8266 which uses only 20uA in deep sleep.

This makes a huge difference for sensor systems etc. A pico/RP2040 cannot be powered by a battery for very long.

I never tried to explore the Pico deep sleep indeed. I used it with esp32 with great results even if the wake time of 200 ms does not make certain applications viable. Thanks for the point.