I think the conclusion is erroneous from the simple fact that the highest biodiversity hotspot on the planet is the tropical Andes - 15,000 endemic species of plants, mostly located in cloud forests above 2000 m
Having no biological education beyond schoolboy level (back in the '70s!) I may be completely wrong here but it seems to me there is a potential hole in your argument.
You are equating current biodiversity in two or more locations with rate of evolution in those locations. Although this may well be valid it is not guaranteed to be.
Suppose in one location you have evolution happening at a rate
x and it has been happening for a period of time
t. In a second location place the rate of evolution is
x/2 - i.e. half the rate - but it has been happening for
10*t - i.e. ten times as long.
All other things being equal - which of course they never are - you could reasonably expect the second location which has half the rate of evolutionary change but has been doing it for ten times as long to have the higher current biodiversity.
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