> That would be science.
In the broad sense, the sciences include philosophy. Natural or empirical sciences are not privileged. They are a product and part of culture as much as anything and thus subject to the same caveats as anything else. Those who worship at the feet of "Science!" are those who lack the intellectual sophistication to understand what science is. It is a kind of petty intellectual provincialism when elevated beyond its natural place in the grand scheme of things.
So yes, religion, and philosophy (metaphysics at its core), are very much concerned with ultimate reality. This does not mean that what the sciences tell us must be false or illusory, only that, at best, they are concerned with bits and pieces of reality, while metaphysics studies being as being and religion, at least Christianity, concerns itself with revealed truths concerning the ultimate. Faith (as probable and trustworthy) only enters the pictures when, for example, we identify the god of Abraham with the god of philosophy (Ipsum Esse Subsistens). I.e., the god of revealed theology with the god of natural theology.
So while the empirical sciences are without question a good, let us not pretend they are anything more than they really are.
> Religion is a set of rituals, values, traditions, beliefs, institutions and power structures which claim to have a supernatural justification. Since the supernatural justification cannot be examined, it cannot really be questioned or investigated.
First of all, there is no single thing called "religion". And furthermore, every man has a religion according to the most sensible characterization as that which a man worships. All men worship something, view something as the highest good, whether they realize it or not.
Second, you've sort of listed a bunch of characteristics without any deeper reflection:
1. Rituals don't exist for their own sake. They have functions. They are a language of signs that are meant to communicate some reality and put some flesh on things which could otherwise remain purely abstract. They can be sacramental in nature (sign of the cross). Truths are what are ostensibly communicated, and it is those truths ultimately that they serve.
2. Traditions serve to maintain a continuity that allows truths to become accessible across generations (and btw, there are traditions within science as well; you couldn't have science without tradition; what do you suppose a mentor is doing when he's teaching you?). Tradition is what allows you to interpret scripture. Without that knowledge, you're left with the problems plaguing Protestantism (obverse the 40,000+ sects in America alone). So again, truth is the ultimate end of tradition.
3. Institutions also serve a purpose. They are guardians of tradition and, in the case of the Catholic Church, also that through which sacraments are dispensed. Institutions are also not solely the province of religion, at least not from a Christian POV where a distinction between God (religious) and Caesar (secular) exists. But again, truth is the ultimate end.
4. "Power structures" is a wishy washy term in this context. Authority exists everywhere. Distributions of power exist in all human societies. Authority has a purpose when exercised within its proper bounds, which is the good of men in some sense, and ultimately the good of men depends on truth. Again, we are oriented toward the truth.
The truth as known and the truth as lived.
> Imagine some historian proved that Moses never existed. Would Christianity, Judaism and Islam just disappear? Of course not.
This is untrue. Religions make truth claims. Which truth claims are essential to the viability of a religion and in what way vary. Something like Buddhism would probably survive without the Buddha of the stories because the principles are what count, but it would not survive a thorough rebuttal of those principles. On the other hand, Judaism and its heir, Christianity, for example, are historical. God acts in history. There is historical development. That doesn't mean that the writing style used in heterogeneous scripture will conform to modern historical conventions, that there aren't places where symbolic language or hyperbole are used, but it does mean, for example, that Christianity as such is nothing without Jesus. Jesus was not just some "wise man". The validity of Christianity rests entirely on him being the Incarnate Logos. Otherwise, Jesus was a lunatic, a liar, or the gospels are made up (to all of these, and more, there are responses; see Kreeft for a compilation). So yes, if you could somehow show that Jesus never existed, you would in effect destroy Christianity. There is no question about it.