Interesting. In the higher end of the racing
world, polars are considered gold.
The frustration expressed by the OP may be caused in part by a misunderstanding of how polars function. The polar is not a prediction of top speed. Rather, it functions to indicate a target speed that should increase VMG. For example, the polar says that in such-and-such a breeze on such-and-such a point of sail, my target speed should be N knots in order to maximize VMG. What this means to a knowledgeable helmsperson is that the boat should be pinched up a bit if the target speed is exceeded, and footed off a bit if the target speed is not achieved.
In my experience, which is admitted limited to racing monohulls, I'm amazed at how often polars have proved true throughout a variety of conditions. The only time I've been frustrated by them is in exceptionally light air, but often this is because of tired sails
, a less-that-perfect bottom, or too much weight in the boat, not because the polars have predicted the wrong target speed.