PlanetSide 1 handled scale much better than PlanetSide 2, sadly far fewer people got to experience PlanetSide 1 in the brief period between it being awful and being awful. You could really get fights of 400+ going and just looking up from a trench at all the weapon spam and aircraft was intense, no culling.
It's not hard to make a FPS with a huge player count, it's just that the skills have been lost. Big FPSes used to run over dial-up back in the day and you have literally 20,000 times the bandwidth today, but it gets wasted by an aversion to writing networking layers, devs go with engine-provided networking and various high-level concepts like RPC and replicated variables. Rather than the careful design and quantization of the past, you'll find bloat squeezed through oodle today.
For an example of how things used to be,
Dynamix's programmers wrote up some of the networking model for Starsiege: Tribes (and Tribes 2) here. This was a game that did 128 players over dial-up, had high-speed physics, long-range ballistic weapons, base building, a huge (for the time) map, multi-seat vehicles, etc.. It's a good read and it's still applicable today, the only thing missing back then was lag compensation but that doesn't change the fundamentals. A unique property of it, sadly not covered, is that the client-side prediction could predict acceleration, not just velocity. You could see this in action if you lost connection, vehicles that were turning would fly in circles until the game admitted the connection was gone for good. Was a really impressive pile of tech, the game was also the first I can remember that had IK feet.
robertsspaceindustries.com
