They're also expensive. At least last time I priced them out, they cost more than the radio and MCU.
(Also, you’d probably just use one of those 32 bit ARM chips nowadays).
[1] I don’t have an encyclopaedic knowledge of the AVR range and haven’t looked at in a couple of years, so I’m sure some of the advanced stuff is available on Mega models.
https://eu.mouser.com/ProductDetail/STMicroelectronics/STM32...
There are probably even cheaper ones