The trouble with the pie charts here is that you get no sense of the "natural" variability. Moreover, you have four consecutive individual years (one of which is a half-year!) compared to a full decade (with a bunch of intervening decades missing).
For a decade-by-decade comparison see this image from a Skeptical Science article:
Admittedly, the decade-level averaging makes it less dramatic, but the trend seems clear enough - the last two decades are certainly much further away from 50/50 than you'd expect by chance, especially the last one. You can also get the sense that having maybe a 25% excess of either highs or lows over a decade might represent a chance fluctuation, while a 2:1 ratio seems almost impossible to explain away as a fluke.
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