I have a theory on this.

Yes, sugar breaks down to the same fructose and glucose proportion.

That takes months. Even longer in concentrated syrup form. Even longer in the one of two components that bottlers get to make the syrup.

A freshly bottled coke in a glass bottle still has the undivided sucrose and that is why it tastes more crisp. After a while, it separates and it doesn’t taste any better because it physically isn’t different.

A freshly bottled HFCS coke still tastes fresh in all other respects, but is essentially stale on day one as far as the sweetener goes.

But by far the best is a properly calibrated soda machine with fresh syrup— but it’s only really fresh if it is sucrose. Otherwise it’s basically stale before you even make it.