That's true. You could standardise on JSON with comments removed by JSMin... The underlying data would still be standard.
Yes, the sysadmin was clearly at fault. No, this is not a deal breaker, as seen by the longevity of Sendmail. But a config file that gets pushed through a preprocessor has a more complicated life cycle than a "static" equivalent.
If your organization has comprehensively embraced ansible/chef/puppet/etc this may be a non-issue, because all of your configs might be generated. Just food for thought.
Er, only if the application doesn't run the preprocessor itself.