Dates should be persisted as intervals since epoch where the interval is the finest grain required. This is what enables more sophisticated tools to do sorting and change representations.

But this is a conversation about text formatting of dates. The standards for this are well established. Yes, padding is required and assumed.

Humans think day/month or month/day, they have absolutely no interest in reading the year first.

Humans prefer what is familiar. Speaking as a human, for me that’s ISO 8601.