| spec | ATSAMD11 | ATmega4809 |
|---|---|---|
| SRAM | 4 KB | 6 KB |
| flash | 16 KB | 48 KB |
| EEPROM | No | Yes |
| 5 V compatible | No | Yes |
| I/O pins | 22 | 41 |
Regarding the memory, also consider that there is significant overhead for the USB CDC stack. In fact, the "MuxTO" firmware that provides the UPDI programming and CDC passthrough capabilities on the Nano Every doesn't even fit in that memory when compiled with the latest version of its hardware package. So not so much underutilized as you might think!
Sure you can find some specs that are superior, but it's certainly not accurate to claim they all are.
But I do think the ATSAMD11 is a very interesting chip since it has good support by the Arduino ecosystem and is available in an IC package that is easy to hand solder. In addition to the Nano Every, Arduino also uses it on the MKR Motor Carrier. It's really cool to me that the firmware in both these cases is an Arduino sketch, and thus very accessible to the Arduino community for tinkering.
OK, first of all, the SAMD51 is something different. That is a much more capable chip. Adafruit has embraced that family and provides nice support for it via their "Adafruit SAMD Boards" Arduino boards platform as well as CircuitPython
But as for programming the ATSAMD11 with the Arduino development software, the answer is also "yes!" There is this nice 3rd party boards platform:
That is even the one Arduino uses for the "MuxTO" and MKR Motor Carrier firmware.