I've never found the antipodal argument convincing. Seismic waves converge at the antipode of an impact only if the target is spherically symmetric and isotropic. In the actual Earth, you have reflections off all kinds of laterally varying boundaries. Also, the sound speed differs substantially between continental and oceanic crust, so the path matters quite a bit.
The Chixulub impact is also not that big (as planetary-scale impacts go). The projectile was what, 10 km? Shock heating is only significant within a few times the projectile diameter.