In fact if you want more than say 250kB of RAM, currently the cheapest alternative on Mouser is ~$5 (STM32F730V8T6TR). And that will have less flash!
Yes, it is not a replacement for ESP32 but it isn't supposed to, it is placed squarely between arduino and ESP32 power-wise
Yes and no: with the STM32 you don't necessarily need an external flash chip (= significantly less PCB space consumed) and you get a lot more integrated high speed peripherals than the RP2040 has, including 50MHz SDMMC, 50Mbit/s SPIs, 27Mbit/s USARTs, and proper 480Mbit/s Hi-Speed USB 2.0. The STM32 is also significantly faster (216MHz), uses a Cortex-M7 instead of a Cortex-M0+, has a memory protection unit, and so on. The RP2040 is a toy in comparison.
It really depends on what you need for your project. Sometimes that weird RP2040 can be the perfect choice for a project, sometimes an even cheaper STM32 could be an even better choice, and sometimes you need a powerful chip like e.g. that STM32F730V8T6TR.
Though IMO, the most interesting chips here are the Cortex-M22 or Cortex-M32 chips (from everybody). These chips have outstanding features at under 5mA of power usage, albeit more expensive than your typical M0+ chip.
M0+ like RP2040 is always about cost-optimization. But capabilities wise, there's all sorts of other processors that simply does more in smaller power envelopes.
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Thinking things like Nordic Semiconductor's nRF5340.
RP2040 has an MPU as well, just FYI
Also, good luck GETTING an STM32H7/F7. I've had an order outstanding for ~13 months, expecting parts in 3 more moths. All this while i was able to buy RPO2040 trivially. There is something to be said for actually being able to GET the chip, even if it is not the perfect tool for your job.
Cortex-M4 is the "smallest ARM" with an MPU IIRC (Or was it M7??). RP2040 is Cortex-M0+ which shouldn't have MPU, from my memory.
C-m0+ has an optional MPU: https://developer.arm.com/documentation/dui0662/b/Cortex-M0-...
RP2040 has it: https://datasheets.raspberrypi.com/rp2040/rp2040-datasheet.p.... (page 76)