RAM is fast, but volatile (i.e. data does not persist through loss of power. you turn off your pc, you lose all your RAM).

SSDs are slower than RAM, but you get non-volatile storage (the NV in NVME). That is, the data persists through power cycles.

If you can invent non-volitile storage with the performace of ram then you could make a lot of money. If you want a RAM-less design, I hope you're happy with a multi-minute boot up time for each app.

You can easily set up a RAM disk in Windows or Linux - an area of storage which appears to the OS as a storage device, but uses a reserved area of RAM to store the data. You could play around with that to see the performance difference between a RAM disk and a regular disk. You get a massive read/write boost at the cost of reduced memory for the rest of the system, and volitile storage as above. Now imagine the opposite: all memory reads and writes would be reduced by the same degree in a RAM-less system. Check Task Manager to see how much memory I/O is going on at any time - it's a lot.

You could also force your machine into Swap by using one app to fill the whole of RAM, then using the swap file on disk as the overflow. See how system performance feels under those conditions. It's really bad.