Security is important, and we agree that removing that would probably be best. However, any 'hacker' would have no problem detecting your site is Joomla. There's no way to hide it.. heck, just looking at the robots.txt file is probably the easiest way to tell the site structure and definitively tell it's Joomla.
Either way, I've taken note of this as we have plans in either the 5.2 or 5.3 release to overhaul our CSS class names for better semantics and use improved Bootstrap styling. This should be done around that time.
I hope that helps explain, but if you have any other points, definitely let us know. We take security very seriously!
Thanks,
Alex