A few notes:

1. "For the atheist ... we simply exist ..."

I don't think you grasp how self-contradictory this statement is. There is no such thing as "simple existence." At the very least, "simple existence" would require the non-existence of time. Time means movement; and movement necessarily means purpose. Purpose is another word for meaning. To the extent that atheism overlaps materialism -- quite a bit, I'd guess, for most atheists, anyway -- the only outcome is despair. Chesterton, in his book, "Orthodoxy," wrote about this pretty eloquently more than a century ago.

2. "the individual ... has the sole power to define themselves ..." "the subjective is more important than the objective ... in defining individual reality."

The idea that we can "define" anything, in some objective sense, truly is absurd. All we are capable of doing is describing our experience. Definition is a device used to manipulate apparently closed systems, but its utility is relative even there, inasmuch as there are no closed systems (Gödel). It is conceit and self-deception to conflate description with definition. Sadly, nearly everyone does it without realizing it.

3. I don't think you cast your net of criticism broadly enough. Don't you think it should be an indictment of all religion? And, in doing so, you may be unaware of the importance of the distinction between objective description and subjective experience. Religion is the outward form of an inward experience; and when that outward form is turned in upon itself, made prescriptive rather than descriptive, the door is opened to all manner of evils. I suspect the problem you have with Christianity lies here.

One of the tragedies in this apparent conflict of spiritual experience is that antagonists almost always throw out the baby with the bath. In my experience, the truth and meaning of Christianity lie in its simplest expressions: Love one another, etc. When Jesus was asked the most important commandment, you know what He said: that the whole of the Law and the prophets were contained within two simple rules, both of which were to love. Finding truth within Christianity, or any religion, does not validate the entire framework. Religion is a means to an end, not an end in itself.

There are no closed (rational) systems; and meaning, purpose, comes from outside the system. This is the realm of spirituality. Religion lies in the realm of the rational. Man is a creature of both matter and spirit, on a lifelong quest for an ever-increasing revelation of meaning. In Christian terms, that meaning is love, or God Himself. This is not objective religion; this is subjective relationship, the only real Truth there is.