It is my own belief that Nizoral is way overrated and that its positive effects on the hair are marginal at best. The reason it is in the big three is mainly to do with convenience, as it is a shampoo and is convenient to use alongside the other two ingredients of the big three.
If Nizoral really was so effective, there would be much more evidence of its effectiveness from these forums, especially from the success stories section. And of course, there would indeed be no need for finasteride. These hair loss forums have been around for well over a decade, and many thousands of forum users (myself included) have experience of using Nizoral, and in all this time, there has been very little evidence that it is anything like as effective as some of those studies seemed to suggest.
In any case, I personally am highly skeptical of those studies that found Nizoral to regrow all that hair. From what I've read, all of the studies carried out on Nizoral as an male pattern baldness treatment were performed on a small (and in some cases, tiny) sample size, and most of these studies seem to have been carried out by people to whom the outcome of the results mattered. I suspect that there may well have been a fair amount of experimenter bias in these studies.
I'm not saying that Nizoral is useless. I think it is a good idea to include it in your regimen (as long as your scalp can cope with it), as it is so little hassle and there is nothing at all to lose by it, but it should not be thought of as the main weapon in your regimen, but rather as a secondary (and when I say secondary, I mean very much secondary) add-on to finasteride or dutasteride.