So I am making an app CellMon to see the signals.
What this tells me is that my 4G/lte is usually on 942MHz (sometimes in other low bands), and has a typical strength of 45% at home.
3G/umts is always on 2600MHz and strength ~= 10% at home. In particular, the fringe areas that now have no functioning coverage, are surrounded by bush. 2600MHz would be expected to be very heavily absorbed by bush, so this really explains why voice call range is now so poor.
VoLTE is needed not because there is no 3G, but because it is now unusable in many areas.