This sounds like a footgun.

At some point some application developer will introduce a bug where they're not sending utc.

Without the time zone, the wrong times will end up in the database, bad data mixed in with good. This will be a nightmare to fix.

With the time zone, I don't think this class of bugs is possible. Most application developers will wrap the time in an object that allows them to do time operations without needing to directly handle time zone in most cases.