Wrath of God also has strikes against it in that the cheaper and more splashable Fire/Ice and Rack and Ruin are just as likely to be able to kill more than one creature.
Exactly. The traditional benefits of Wrath of God are:
1) Kills ideally about 3 or 4 creatures all at once. This doesn't happen in our format, as there traditionally aren't more than 2 on the board at once, and even 2 is a stretch. Aggro that plays more than like 2 creatures is nonexistent, barring Kowal's Madness, or the never-talked-about-less-often-than-that-played Oshawa Stompy.
2) Kills large creatures that, say, Pyroclasm can't hit. It just so happens that the large creatures are also artifacts, so Rack and Ruin is just more versatile in that respect.
3) Kills untargetable creatures. We don't have any of those right now.
4) Deals with annoying protection from X and regenerating creatures. Again, none of those are to be found in Vintage at the present time.
I don't think that Wrath is necessarily a terrible card in Vintage, it's just that none of the traditional benefits of Wrath apply. This makes it very difficult to justify the sorcery speed and double white committment for a card that doesn't do anything more than something that costs 2 or 3 mana already does. Don't forget that those 2-3 mana options are wishable. You know how that old "strictly better" thing goes. Wrath of God is just suboptimal, not necessarily terrible (terrible means much worse than simply "not good").