Nw as I came to think of, it might indeed be that there are some people who do not know the internals of cellular networks.

It might be that I am glossing over some bits due to the very usual mistake that people make, assuming that other people already have the basic knowledge because everyone around me knows these things.

So, here is really quick introduction to the different ETSI-GSM generations;

2G, original GSM
First wholly digital cellular radio system. Originally designed for voice only, later enhanced by services like SMS messaging and IP calls.
Air interface is based on a slow frequency hopping scheme, with TDMA interleaving with 8 timeslots.
Much of the network intelligence resides in the core side, BSC and MSC elements. BTS is fairly dumb device which only really connects the air interface to T1/E1 SDH links. The backhaul is SDH and ATM.
The reason why it is not practical to have simultaneous CS and PS calls is primarily the limited bandwith of the air interface and secondarily the routing of the backhaul T1/E1 to specific network element that is used to route the PS call to internet.

2.5G, enhanced "Edge" GSM
This basically adds possibility of allocating more than one timeslot per UE, so that downlink data rates can be doubled or quadrubled.
Of course this also limits the number of UE's in the cell accordingly.

3G, WCDMA UMTS
3G is a logical continuation of the ETSI spec and can coexist with 2G well but it completely overhauls both air interface and backhaul.
Air interface is based on fast frequency hopping by code spreading. Signalling is very complex and there are huge amount of different options and tunables.
BTS is more intelligent than on GSM, transferring some BSC functions to the edge. Backhaul is ATM and the rich signalling allows simultaneous use of several logical channels which means for example CS and PS calls.

3.5G, HSDPA and HSUPA extensions
Small enhancements which are basically just software tweaks in signalling to group logical channels so that data rates can be increased. HSDPA (=High Speed Downlink Packet Access) is the more common 3,5G technology, HSUPA which is the same thing for uplink direction is a bit rarer feature.

4G, LTE (Long Term Evolution)
This again revamps both air interface and backhaul, where CDMA is now dropped for ODFMA and ATM is finally put to rest and IP goes directly down to BTS.
Signalling is actually simpler than on 3G which was really an elephant on that respect, still more intelligence is distributed towards the edge and the BTS is now handling quite lot of things by itself.
Because SDH/ATM has been dropped from the backhaul CS calls are no longer possible and indeed thare were emerging operators that had no telco legacy and implemented VoLTE-only networks.

5G
This is really more or less an umbrella standard covering a wide range of modulation and spectrum allocation technologies for different use cases. (everything between very low-power/low-bandwith IoT gadgets to super-low latency factory automation and autonomous vehicle control and super-high bandwith for media terminals) Like 4G this is also All-IP network and again more intelligaence is pushed toward the edge, so BTS sites will have cloud-computing resources for some nice new functionalities and services.

To recap; all evolution of the ETSI-GSM networks has been to the direction of pushing more and more functionality and intelligence from the core towards the network edge. Because the air interface is the "last mile", everything can be done faster when the processing is nearest to UE and signalling is done in the BTS to minimize the loops done via the backhaul.