Error in reasoning. Post-Hardcore is perhaps another variant of Hardcore punk, because it cames from Hardcore punk. But if Lacuna Coil was a Gothic METAL band, they cannot be a Post-Gothic ROCK band, because they never played Gothic ROCK. Thus they're a Post-Gothic-METAL band. That's a big stylistical difference. Lacuna Coil's music shows no roots in Post-Punk music (the true origin of Gothic Rock). Their music is a simple variant of "Alternative Heavy Metal Rock".