"Tallest" measured from base to summit is a controversial way to measure "tallest." There are rocks underneath the soil around Everest. Why don't they count when the rocks underneath the water around Hawaii does? Anyway might just want to put a caveat.
Surely if you're going to count the rocks underneath mountains you can keep on going until you reach the mantle? I could be wrong but I always thought that tallest has meant from the base of the mountain to the top.