I've never had any of my hard-points rip out or even loosen up on any of my planes or planes that I have built for others Hydro. Besides being secured with glue, each hard-point is smaller in diameter than the horn above it and its cap below it so it really is locked into place. I've even used used them on flying wires, struts and under engine mounting bolts without failure. Having said that,
I am a firm believer that as in all aspects of building, strength comes from well fitted joints along with good glue penetration. So in other words if one is relying on the glue to hold a hard-point installed in a hole that was drilled too large, then all bets are off!
I like your idea of tapered holes, but for me, making clean straight holes in balsa is challenging enough...lol
