This is a commonly heard idea. One variation is, 'The longest sober person is the person who got up earliest this morning.'
Sobriety lengths are not reset every morning. Duration is a recognised phenomenon. For instance, we have birthdays. We do not claim to have been born afresh each day.
The aim might be to counteract the notion that length of sobriety automatically confers authority or entails the possession of knowledge (although it does automatically entail the possession of experience). This is certainly a notion to dispense with. However, the way to do so is not to deny that length of sobriety exists but to challenge the false assumption concerning what it confers or entails.
Sometimes it is implied that there is no such thing as knowledge or experience, they cannot be acquired, or, if they can be acquired, they are of no use. People literally share, 'I know less now than I did when I came into recovery', 'I'm no further away from a drink than when I came in', etc.
Fortunately, knowledge and experience exist, are acquirable, and are valuable.
It is certainly the case that length of sobriety does not automatically confer knowledge or experience and does not itself protect against hubris or folly; however, all other things being equal, and the many exceptions aside, people sober longer do tend to have more knowledge and certainly have more experience.