No, that's a lot more, especially with more complex obfuscators. They can generate an IL that cannot be expressed in most languages, and where the logical flow is terribly confused to confuse the best tools. With a lot of time, you can do this (perhaps a lot by hand), and of course the arms race between obfuscators and deobfuscators - but you greatly underestimate the technology here.
Also note that many obfuscators look at the entire application (and not just at one assembly), so they can also change the public API.