I suspect you're actually misidentifying the culprit.
Lag is generally not noticeable on cellphones, and lag has always been a problem with landlines on long-distance (especially far-international) calls.
What you're describing "like a walkie-talkie" is actually the difference between half-duplex and full-duplex.
Landlines are full-duplex, and cell phones were notoriously bad half-duplex... until 4G which is considered full-duplex. There's also the issue of carriers muting audio completely when it's under a certain threshold, which makes them less responsive, because you have to ask "are you there?" every so often.
Videoconferencing latency is a separate issue, because there's one central server for each meeting, so if it's between the NY and SF office, the server may be in SF, so two separate NY participants get double the latency talking to each other than they do talking to SF. But, everybody hears the same audio.
You might say, well why don't they select a server in the middle of the country for that call then? But selecting an optimal server location for a videoconferencing call is difficult, even if you have access to cloud locations all over the country/world, because you usually don't know in advance who's going to join the call. So whoever hosts the call or whoever's the first participant, the server is often chosen to simply be whichever one is closest to them, which can sometimes be quite suboptimal once everyone's joined. (And I sure wouldn't want to be the one to write code for switching servers mid-call.)
Also, videoconferencing is much closer to "half-duplex" because if you were always mixing everyone's audio together, it would be a noisy mess.
But in conclusion -- latency/delay isn't a significant new problem that digital networks have introduced. It's always been there, but duplex, silence thresholds, and conference calls are the more important factors to pay attention to.