I'm working on a state wide radio system for a power company, its a simulcast network, with 20 talkpaths. Your worse case bandwidth utilization is on the order of roughly 1.5 megabit a second per site (realistically, its much lower). In addition, if a site fails the other ones will still function, also, if the network core fails, the sites go into a failsoft mode, which allows single site communications to still occur.
FirstNet is based on LTE. Last time i looked into it, it was a private LTE network, with the ability to piggy back on public LTE when there's no private coverage (with a high priority). So you can forget about the simplicity of a basic PTT network. Here, it's MCPTT (Mission Critical Push-To-Talk), which is a layer on top of LTE leveraging the LTE multicast support (eMBMS) when applicable. So not exactly super simple.
There a protocol extensions for public safety on top of MCPTT. To better handle out of coverage situation (D2D or ProSe, which is device-to-device communication with relay support too), to hook custom applications on the network side, etc. But the infra is LTE, so at least it leverages an existing technology. Still, with some additions on top to better support public safety use cases.
And the "obsolete" part is not very convincing. Yes, there's a lot of hype about 5G but LTE will be long lived and perfectly fine for such an application for a long time. I can't comment on the overall efficiency of the FirstNet program, but the idea of leveraging LTE instead of rolling a custom tech or keeping using old and inefficient ones seems sound to me.
I'm working on a state wide radio system for a power company, its a simulcast network, with 20 talkpaths. Your worse case bandwidth utilization is on the order of roughly 1.5 megabit a second per site (realistically, its much lower). In addition, if a site fails the other ones will still function, also, if the network core fails, the sites go into a failsoft mode, which allows single site communications to still occur.