You make it sound like D-Bus is a first attempt and even a hastily put together attempt to solve its target problem. It's not.[1] D-Bus is heavily influenced by (and intended to replace) DCOP, the communication system used by KDE 1 and KDE 2. DCOP was widely lauded as an extremely well-designed system.
[1] https://en.wikipedia.org/wiki/D-Bus#History_and_adoption