Hmm, not quite. First of all, it's important to remember that the Lutheran reformation was not a one or two-man operation, but really the Evangelical Catholic churches in the region of Germany, with everyone coming together in a joint evangelical confession - which can be boiled down to the article of justification by faith apart from works. Luther and Melanchthon were certainly front figures, but it's not like they were some kind of Lutheran popes dictating a new belief system, nor were they rivals with competing ideas.
But as you rightly point out, after the death of Luther, there was a time of confusion, with both external conflict and internal controversy in the Lutheran church. Melanchthon, in an effort to form ecumenical bridges, toned down the doctrine of the sacraments, monergism, sola gratia, and approached Erasmus' conception of free will in relation to God's grace. There were some early Lutherans who took Melanchthon's Variata a step further and attempted to compromise with the Calvinists, and for a moment it looked like the Lutheran church would scatter. However, this, what we sometimes refer to as the Phillippist controversy, was put to rest with the Formula of Concord, which united the Lutheran church and is part of our confessions.
So, the general approach orthodox Lutherans take to Melanchthon is similar to that of the Church Fathers, such as Augustine, for example. We fondly remember and appreciate most of his work, but we won't compromise on the Gospel. For whatever it's worth, my personal feeling is that Melanchthon, in his own mind, probably didn't compromise on the Gospel, but he obsessively formulated a confession that could be taken in two ways, which is not too helpful. I don't think he radically developed his own theology, so I don't think it's accurate to understand Melanchthon's writings as drastically opposing that of Luther's, but he was convicted by unity. But, regrettably, unity based on indifference is not true unity. Yet, even though we can't produce perfect doctrinal unity, given that sinful mankind are by nature schismatic, we can take comfort in that Christ is the one who produces true unity in Himself.
