This close tab behavior would indeed be fantastic if the most important tab behavior use case was "user should be able to close multiple tabs in rapid successio

This close tab behavior would indeed be fantastic if the most important tab behavior use case was "user should be able to close multiple tabs in rapid succession using the mouse." But really, how often would a typical user need to do that? There may be a good reason to eschew prevailing Mac UI conventions and to put the tab close button on the right, but this isn't one.