Engels tackled the radical reformation through a revolutionary lens. He insisted on comparing the peasant uprisings of the sixteenth century to the revolutions and restorations of 1848-50, arguing that the two failed revolutions followed a similar pattern. In 1848, the petty bourgeois fell out with the proletariat, leaving the masses isolated and leading to outcomes that favored the "princes" of Europe, rather than the people. Similarly, Engels believed that the broad revolutionary movement inaugurated by Luther, in which many oppositional factions came together to oppose the excesses of the catholic-imperial regime, similarly fell apart when Luther and the middling elements of society who favored moderation, like the burghers and the low-level nobility, softened their previously more radical positions in favor of reconciliation with the prevailing order; a reconciliation which would bring only cosmetic changes to the papal-imperial constitution without dramatically reforming the feudal society.
Engels compared Luther unfavorably with the far more radical Thomas Muntzer, who advocated the total abolition of class, caste, and private property, the confiscation of church property, local election of clergymen, and the abolition of the Holy Roman Empire itself in favor of a unified German republic. Unlike Luther, Muntzer had an ear for the tones of the peasantry, and Engels believed that Muntzer crafted what was in reality a radical political revolution in the language of religious prophecy that his pious but uneducated followers would better understand.
I feel as though I've seen this story many times, reading leftist accounts of the Spanish Civil War, the Russian Revolution, the 1848 Revolutions, and now the Peasant War. The initially radical revolution is betrayed by conciliatory elements within it that take the wind out of its sails and adjust its goals to align with the power structures of the time, rather than to overturn them. This is either a trope of lost cause leftist historical revisionism, or all of these accounts have come across an elemental conundrum: the near-futility of revolutionary change.