yep. as noted in https://news.ycombinator.com/item?id=8648995 it wasn't even just dcop - KDE had tried CORBA before switching to DCOP, and GNOME of course tried CORBA (two different ORBs), then tried Bonobo-on-top-of-CORBA, and SOAP. There were tons of documented protocols on top of X11 (many still in use today). And that's ignoring the countless ad-hoc solutions that various apps used...
Linux desktops are implemented as process swarms and communication among processes is one of the central things they have to deal with.
It isn't better than those categorically. But it's definitely better than them for building a multi-process desktop.
"better" depends on what you are trying to do.
Of course CORBA and SOAP are considered old and horrible now, 15 years later. But currently-popular stuff is in many ways equally unsuited to coordination of local desktop processes, because it's not designed for that.
Linux desktops are implemented as process swarms and communication among processes is one of the central things they have to deal with.