If anything the server-side coding is harder. Many games do the full physics/simulation on the server to minimise cheating, and have to simulate from every player's perspective. Meanwhile the clients have a single perspective and most of the computation effort is offloaded to the GPU.
Additionally, most multiplayer games have the same codebase for the server and the client for the obvious reasons. Single player is literally "online play" with an in-memory channel to a local server.
All Quake-based games work this way, including the derivative Source-based games and a bunch of other engine variants. Unreal works this way too if I remember correctly.
You can't realistically write a client in C++ and a server in Java. You'd be practically doubling your development time!
Additionally, most multiplayer games have the same codebase for the server and the client for the obvious reasons. Single player is literally "online play" with an in-memory channel to a local server.
All Quake-based games work this way, including the derivative Source-based games and a bunch of other engine variants. Unreal works this way too if I remember correctly.
You can't realistically write a client in C++ and a server in Java. You'd be practically doubling your development time!