If the argument that Doom killed the platform is valid, it can only be true for gaming (which was a very large portion of home use). After a great headstart, Amiga fell behind in many other areas: business and productivity software, networking and collaboration, multimedia and realtime-3D graphics.
And regarding gaming, let's not forget that the SNES and the Sega Megadrive/Genesis were going strong when the Amiga was fading away, and it took a while for them to get a version of Doom.