[hwillis]

Here's a video of this test being performed on another frame: https://www.youtube.com/watch?v=BCU7VT9fOpo

With a 20 cm drop the velocity is 4.95 m/s, or a pretty average bicycle pace (11 mph, 18 kph), ridden directly into a wall. All things considered, a 4-5 mm deformation isn't that bad. As long as it isn't splintering or splitting, which would be dangerous, the bike isn't going to see much forces in that specific direction. Rider weight doesn't matter because the rider will immediately be thrown over the handlebars.

In more realistic scenarios like hitting a curb or dropping the bike, the force will be much more vertical, which will give a several-times-higher mechanical advantage due to the fork rake. The tires will also absorb a lot of the shock loads.

In general wood doesn't lose strength from being beat up, no. Wood construction standards (which admittedly, I know only the basics about) usually assure you that dents and surface defects are not a big deal. The strength in most woods (particularly soft woods) comes from the fact that they're very fibrous and anisotropic, so when they're dented it usually moves the fibers around without actually breaking them.