I certainly wasn't saying that one *replaces* the other. However it's *perfectly* valid to compare the *tradeoffs* between them.
You even do it yourself in the second paragraph:
"This stuff is useful in a few cases however which SELinux doesn't really cover: it's trivial to write for admins,"
I think "trivial to write for admins" is less true than you think. And of those issues are the same reasons that writing SELinux policy is hard; version skew of the "app" and the underlying system, delta between tested configuration and deployment, etc.