Elephants very likely could be more intelligent than us, it just seems that intelligence is a difficult thing to measure quantitatively.
We have very good problem solving ability of course, but a superpowered ability to ask others how they solved the problem. If we wanted to somehow define a kind of 'brain horsepower' type intelligence, it seems to me that the former is closer to it than the latter, and it doesn't seem obvious to me that humans would necessarily take the top spot. Or that there's a reasonable/ethical way to test it -- let's take a human, elephant, crow, and dolphin, raise them in total isolation from the any community to get a measure of their untrained intelligence... we might get some interesting results on intelligence, but mostly we will learn something about ballistics as some ethics review board launches us unto the Sun.
I suspect the question really doesn't make sense if that is true.
We just have this bias/mind projection fallacy that intelligence is a general physical property of the brain that can be measured. I just suspect this is not true.
Like athletic ability doesn't generalize well. Of course, someone not athletic at all is never going to be a great athlete in anything but it makes no sense to compare Lance Armstrong to Patrick Mahomes in some general athletic context. Putting a number on a general athletic ability index between the two would just be total nonsense.