It’s probably because running such old hardware means your daily usage wouldn’t show much difference between the 2 setups. If you mainly browse the internet or play gpu boumd games, you simply wouldn’t notice a huge difference.

Change that use case to cpu bound games or other cpu intensive tasks and you would likely see a not insignificant difference.

Also newer hardware is more efficient(used to at least), so you should see lower power draw for the same performance or better performance for the same power draw.

So just because you don’t see a difference, it doesn’t mean it’s not there.