The chart module https://www.drupal.org/project/charts → provide an API to build chart that webform analysis could take advantage off instead of using it's own mechanism. One advantage is the chart lib is then swappeable. It's also better to have one chart mechanism on a given website.
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This could be a nice feature, but it adds dependencies and makes it harder to get the module to work (more configuration is needed before the module starts working). So there should be the option to choose between using the Charts API or go with the zero-config/built-in Google charts