Oscar already hit on this, but It's not just "comparing and contrasting", you look for patterns and relationships, which is what all science does. So, for example, proponents of 'modernization theory' noted how there was a strong tendency for governments to undergo democratic transition once they reach a certain level of economic development and income. Each democratic transition is a 'non-repeatable' event, but that does not preclude one from systematically analyzing which variables correlate to which outcomes, using sophisticated statistical techniques which are able to control for variables not being looked at. You have an extraordinarily narrow view of what counts for science, and an extraordinary ignorance of what modern social science does and its methods.
As for bias, why don't you actually bother to read the material, and see whether 'bias' is as big of a problem as you predict. Social scientists are very conscious of 'bias', hell I could give you multiple books dealing with social scientific research design dealing with this very problem. There are plenty of strategies for minimizing it, just like in the so-called "hard sciences". You seem to be under the impression that all of social science is bogged down in petty partisan bickering or something, or just writing polemics. In fact I know you've made such commentary before, so your new found respect for the "arts" is you turning a new leaf, because previously you've done nothing but disparage economics and political science.
"No doubt you are aware that Marx predicted revolution in the highly industrialised countries with large proletariats, certainly not Tsarist Russia"
Yes so that prediction didn't take place, Marx acknowledged that the center of revolution was shifting in the Russian preamble to the Communist Manifesto, so that means that social science cannot make predictions? Lenin made modifications to that theory, incorporating the importance of imperialism and the "weakest link in the imperialist chain". Theories get amended when the results don't match up. This happens in so-called "hard science" too. I don't get your point. Talk about throwing the baby out with the bath water.
If you want examples of successful (and modern) social scientific predictions, consult the work of Bruce Buena de Mesquita. He is a political scientist widely consulted by government officials for his predictions, much more so than any area specialist.
"To claim to be engaged in science does not by itself cut the mustard, even if one is after more grant monies. "
To dismiss work without being knowledgable about what it involves doesn't cut the mustard, and can't be taken seriously. It's especially ironic considering you supposedly care about rigor, but can't be bothered to get up to date about what you are criticizing. It's just being narrow minded for its own sake. You complain about bias when you're the main purveyor of bias.