> very little comedy is truly timeless

This depends almost entirely on the type of comedy. Things like reference, satire, or shock are obviously dependent on the specific context of time in which they were made and of course become less meaningful as times change.

But comedy is not inherently less "timeless" than any other art. Who's on First is genuinely still funny almost a century later.

The little bits of surviving ancient comedy may seem trite but being simple does not make the jokes less "timeless".