I don't see people carefully mix their liquor in the exact same proportions as beer and then drinking at exactly the same rate, so your argument is about as relevant to real world drinking as "if you mix 5% strength beer with four parts water it's basically not going to get you drunk". With or without normal amounts of (typically sweet) mixer, spirits tend to lend themselves to faster consumption and the carbonation in beer also has the property of giving you that buzzy feeling (and that vomity feeling) earlier so you don't feel quite so much inclination to top up.