What are you basing this on other than two fairly weak examples?

What are you trying to measure complexity with?

Why is Montezume more complex than the longer and multiple word John Trudeau?

Same number of syllables in each of first pair.

I might guess that the second, which you call simpler, are merely more familiar to you. After all, for Mesopotamia, Nebuchadnezzar is not a long name.

Chinese names of two thousand years ago consisted of a one-syllable family name followed by a one or two syllable personal name. It's hard to get simpler than that.

Source: People's Names by Ingraham

Chinese-American Names by Louie

A book on Assyrian names that I can't recall the title accurately this minute, but the longest name is a doozy!

Edit: Admittedly, in Western civ there's a propensity to first-name people and change the name, usually by shortening, but that has less to do with simplifying and more to do with asserting social power. "I can call you by your personal name, and I can even control what that is."