I believe there is confusion between units of measurement, numeric values and what is being measured. In your example, the side length of $0.5$ m is the same as $500$ mm. As such, the area is also $250000$ mm$^2$. You can't directly compare the $0.5$ of $0.5$ m and the $0.25$ of $0.25$ m$^2$ with each other as the first one is a distance and the second one is an area, just like comparing $500$ mm and $250000$ mm$^2$ doesn't really give you anything. My example shows that the numeric comparison of different types of quantities can be very different depending on your unit of measurement. As the old saying goes, it is like "comparing apples to oranges".