[Grombobulous]

It seems like the number isn't very useful unless we have a baseline for how often the site is shared at all.

If 0.2% of users share the site via a direct link, and 0.2% of your users share the site via a share button, for an overall share rate of 0.4%, that probably means the share button is worth keeping around.

[yencabulator]

If you assume the that half wouldn't also share it through it other means if needed. It'd need an A/B test.

For example, mobile Chrome has built-in share buttons, no copy-paste of URLs needed, no in-page button needed.