Yes, this means that unlike many C-S architectures, the server is the part nearest the user and the client (may be) further away. But each did its respective job and stuck to its knitting.

Keep in mind that when X11 was first created, and for much of its early life, through the 1990s, it was used for remotely accessing another (or multiple other) systems. The networking capability was baked-in. Nevermind that security was bolted on later, here, have a MAGIC_COOKIE....

You're trying to argue that there should be two distinct pieces of software, a local and a remote renderer, for simplicity.

Rendering does not fit in that space well. The physical resource of a display and graphics card really only allows one renderer to run, so it's not really useful to say "just write two renderers, one local and one remote".

The unix philosophy is not a good argument. It's a principal by which you can make decisions, but it doesn't always lead to good decisions and it's quite open to interpretation as well.