The question is, is that self contenance really joy?
I would apply the classic Orthodox standard to it; does it produce humbleness, humility and submission to the message of God only found within the Church? If the answer is yes, then yes, I would say it is really joy.
Shouldn't joy be like a radiating light, full of life, rather the succumbance to circumstances?
I think it is more about being humble and submitted to God. You are full of life, but it is rather deeper. I find that this sense of joy can oftentimes be more impressive to people than even the loudest, most openly "joyous" person there is. If you read the New Testament or the Lives of the Saints, you will see that most devout people had more of an inner sense of joy. Fun fact: Jesus never laughed as far as we know.
Is that the only joy for us?
I don't know
Is that the only "joy" availlable to us having to conform rather with things rather than try to change them?
Depends on what you mean by conforming and changing. We should conform to God and the faith no matter what the circumstances are and not try to change this at all, but what we should try to change is our vices. We should try to become more virtuous and faithful, changing ourselves for God.
Doesn't that encourage a stagnant non-evolving faith?
God's message doesn't need evolving. Jesus and the Church are the final revelation of Truth to mankind. The evolving we need is to live by this faith and no longer walk in wickedness.