I agree that Christianity should produce joy, and in its own way it did, but not for incarnation and daily life itself (for me). I felt joy in being close to Christ, and I have always felt great love for others (since I was a child) and great love from God. But none of that connected me to being joyful about incarnation. You can be very much rejoicing in your relationship with God, while fully feeling the limitations of being in a body and being rather unhappy about it. From the earliest time I can remember, I felt a bit betrayed by being in a body. It still doesn't feel like me. I just feel now more of an affection for this clunky thing I inhabit, rather than only frustration.
I suspect that much of my need for Druidry was to have a sense of community. I tried for most of my life to go to many different Christian churches, and most were outright intolerant or ignorant of the heart of my own spiritual experience, and none I found ever offered the sort of guidance in an earth-based path the way Druidry did.
The amount of focus on the negative aspects of the world in Christian churches made me despair even further, since I am naturally prone to depression and have no trouble feeling deeply the pain of the earth and living beings under the current malestrom of violence, war, intolerance, and greed. Christianity did not offer me any useful techniques for mastering my own response to these things, to turning down the volume on empathy, which comes naturally to me but can be agonizing. Christianity, as I see it, offered many wonderful things to me but little practical instruction and going to church, at best, feels that I am partaking a wonderful walking meditation. It does not feel like I am fellowshipping with people who understand me.
Druidry offered a community of people who had many of the same spiritual experiences I had and a number of guidances on mastering how I interact with the world in a way that does not deny the chief work of Christianity- the growth of the love of Christ- but is much more specific and practical if you do naturally experience empathy, sense spirits, and so forth (which many Christians simply condemn, as if some of us can so easily switch it off).
In short, the combination works very well for me. Returning to your concept of balance, I rarely found a Christian church that condoned balance. I found many that condoned an almost exclusive focus on the afterlife and attaining heaven, to the extent that even the most basic of Christ's concerns (for the poor, the downtrodden, etc.) rarely made it into the sermon, and forget any rejoicing in the pleasures of this earth. The focus was so often on end-times or on producing guilt by reinforcing that none of us were really good at all, and this may be useful for some but is like pouring salt in a wound if you're already a sensitive, self-reflective perfectionist like me.
In short, perhaps Christianity should be sufficient on its own as my religion, but so far it never has been and the times that I try very hard to fit in solely with Christianity, I end up feeling very much like I am denying my true self and acting in a role. Which then leads to my becoming entirely overwhelmed with life, since it is quite tiring to be acting all the time.
I hope that responds without being too terribly off topic, but I think there is something to it with regards to Satanism. The few Satanists I have met have been the Laveyan sort, and I've had a hard time distinguishing what made them distinctive Satanist outside of using the symbols of Christianity, but turned on their head, so to speak. Otherwise, they seemed like atheistic high magicians, which I mean clearly as a classification. They didn't worship any deities, and they practiced high magic, not unlike some witches.
The little bit I have read about Lavey (interviews and some anthropological articles) made me think he was a pretty normal guy, but kind of ego-centric and really brilliant at marketing. He manipulated the media and Christians because by using the very term "Satanism," he created a media storm that continues to this day, despite his ideas having little to do with Satan in the personalistic sense. A long shot argument could be made that he inadvertently serves Satan since he argues for atheism and self-indulgence, but that's not what the media is normally spewing.
From my understanding, splinter groups that really did worship Satan as a personalistic deity may be more problematic, but Lavey was fairly innocuous on his own. He had children and a ton of pets, and while having an odd house in decor and dressing weird, he did not seem to pose much of a real threat to anyone. In interviews he often stresses that he was staunchly against harming children or animals in any way, because he viewed these as most nearing something sacred, because they were closest to the raw animal instinct by which he advocated living. I never did hear a final word on whether or not his gatherings involved sex, but if they did, it would still fail to distinguish him as being particularly Satanic in the ways the media supposes he (and his followers) were/are.
In short, I think he was very good at manipulating others, and the media and Christians dumbly played along, making him far more famous and significant than he otherwise would have been. It was his use of "Satan" and his tendency to lay all his cards on the media table that led to his infamy, for otherwise, he'd probably be chalked up as just one more weird-dressing oddball from California. Interestingly, so far as I know, no one really knows who the guy was, since he sort of invented himself as a character. I'm willing to bet he'd make a colorful, but ultimately kind of predictable, dinner party guest. But then, wouldn't many?