Before I try to give an answer to your question directly, I want to object to the claim that seems to be its basis. I do believe that recent psychological research about happiness supports at least some elements of what might be called "irrationalism." On the other hand, it seems to me that this same research always treats happiness as a purely subjective property, and I want to make clear that this subjectivist treatment of happiness is very much at odds with the objectivist presumption in most of the philosophical literature on happiness.
To quote myself (the easiest author for me to remember!), "Giddy morons may suppose they pursue their interest by doing what only makes them giddier and more foolish, but sensible evaluation will conclude that such lives are nothing to envy. The addict's high, even secured by ba lifetime supply of intoxicants, is no model of surpassing success in the pursuit of self-interest" (T. C. Brickhouse and N. D. Smith, Socratic Moral Psychology, Cambridge: Cambridge University Press, 2010, p. 46). In other words, one who might be counted as "supremely happy" from a subjective point of view only, could still count as a complete wretch to a sensible objective observer. In the philosophical tradition known as "eudaimonism" (from the Greek word, eudaimonia, which is often translated as "happiness," but which is also reasonably well translated as "flourishing," "thriving," or "well-being"), happiness does have some important entailments with respect to subjectivity, but the achievement of actual happiness will not be exhausted by subjective considerations alone.
But if we take this objectivist stance, it starts to look like the hypothesis that forms the basis of your question may not be one to which we can really give our assent: One who thinks or acts irrationally is not one who seems to us to think or act in a way that is objectively choiceworthy. Maybe thinking or acting irrationally can provide subjective advantages (just think how happy I might be if I could convince myself that absolutely everybody loves and cares about me!!!), but if we (more sensibly, I contend) bring the objective point of view to bear on the question, I don't think we would ever suppose the irrationalism was preferable to rationalism.