The writer talks about some investment misconceptions in investment, among which is "hotspots make more money", "if you even and average out over long periods of time (at least one cycle of 15 years or more), you see that the effect of fast growth in some 'hotspots' areas eventually levels out." What does "even and average out' mean? source: Uncommon sense by Mark Homer.
The specific meanings of even and average out have been covered, specifically "to reach a balanced or middle state between extremes over a period of time" as @TaliesinMerlin posted and calculating the average as you posted. The phrase means that the value is normalized over both time and the values themselves. Simply taking the average may not support the argument since it will be an average of what samples where collected, namely over a particular, possibly limited period of time. Thus, the writer wants to express that the average at a given point or time frame may not support that hotspots make more money on the short-term, but in general they do if you look at them over a long period of time they do. By evening out (normalizing) over time, a more general trend can be observed in a domain that probably suffers from large fluctuations of its averages.