2G defines basic mobile services, for example telephone or SMS.
3G, 4G etc. added internet to it, but there they are interchangeable. Each new one replaces the former if you use only the internet service. But none of them replaces 2G fully.
It's more that all should be backwards compatible, so if you have 5g then you still have 2g and it gives you the bare minimum voice and some scraps of data.
They can reclaim all the spectrum for 3 and 4g (which is a lot) for 5g, while leaving some of the barest functions working for stuff that doesn't need real data.
5g low band actually does, they have down to 600mhz bands which are crazy low with tons of noise shaping, mimo, beamforming and other stuff to potentially bump the snr.
They're looking to add 400mhz bands for even more range, but the low bands have less capacity.