Ok, thanks for the clarification. Even with this new understanding 3G will eventually go. Coverage depends on several things: 1) deployed infrastructure, 2) frequency used and 3) waveform / standard efficiency.
3G can have a temporary advantage for (1). But as the 3G infra ages, it will always tend to be replaced by cheaper / more efficient LTE infra as the existing 3G bands can always be refarmed for LTE. And LTE will make a better use of the available bandwidth. There are large differences between operators on the speed of this process, but the trend is universal.
(2) is why 3G was impaired vs 2G: 2G was deployed in low bands (900 MHz for 2G is very common), while 3G was very often only available in mid-bands (1700+ MHz). The higher the frequency, the more challenging the coverage. So 3G coverage lagged 2G for a long time, and is still lagging in places (Europe for example).
The situation is different with LTE, due to the digital TV dividend. This opened low bands for LTE everywhere (700 to 800 MHz, depending on region). Those bands are even better then the 2G bands. They're not yet fully deployed everywhere (Europe is lagging), but they eventually will. And when it's done you can kill 2G and 3G.
For (3) or course, new tech has improvements so 4G is better than 3G and 2G.
When you combine all of this LTE will replace all previous technologies everywhere, in time. How long it will take will however vary a lot depending on regions. Europe invested a lot in 3G, and telco there will milk this infra as long as possible. And because 3G coverage in Europe is not as good as 2G (see above, bands) 2G will also tend to stay with 3G. Cheap second hand 2G/3G infra will remain for a long time in developing countries. But in the end 2G and 3G will go away, it's just a question of time.
On the other hand, 5G will take a lot longer to replace 4G. The big change is mmWave, but it's for small hotspots. You can have 5G in low bands too, but then the gain vs 4G is small so I expect operators to take their time to replace their 4G infra. We'll have 4G for coverage + 5G for dense areas only for a long time IMHO.
3G can have a temporary advantage for (1). But as the 3G infra ages, it will always tend to be replaced by cheaper / more efficient LTE infra as the existing 3G bands can always be refarmed for LTE. And LTE will make a better use of the available bandwidth. There are large differences between operators on the speed of this process, but the trend is universal.
(2) is why 3G was impaired vs 2G: 2G was deployed in low bands (900 MHz for 2G is very common), while 3G was very often only available in mid-bands (1700+ MHz). The higher the frequency, the more challenging the coverage. So 3G coverage lagged 2G for a long time, and is still lagging in places (Europe for example). The situation is different with LTE, due to the digital TV dividend. This opened low bands for LTE everywhere (700 to 800 MHz, depending on region). Those bands are even better then the 2G bands. They're not yet fully deployed everywhere (Europe is lagging), but they eventually will. And when it's done you can kill 2G and 3G.
For (3) or course, new tech has improvements so 4G is better than 3G and 2G.
When you combine all of this LTE will replace all previous technologies everywhere, in time. How long it will take will however vary a lot depending on regions. Europe invested a lot in 3G, and telco there will milk this infra as long as possible. And because 3G coverage in Europe is not as good as 2G (see above, bands) 2G will also tend to stay with 3G. Cheap second hand 2G/3G infra will remain for a long time in developing countries. But in the end 2G and 3G will go away, it's just a question of time.
On the other hand, 5G will take a lot longer to replace 4G. The big change is mmWave, but it's for small hotspots. You can have 5G in low bands too, but then the gain vs 4G is small so I expect operators to take their time to replace their 4G infra. We'll have 4G for coverage + 5G for dense areas only for a long time IMHO.