I’ve never actually looked at Luther’s famous “95 Theses” before. When I did, I was surprised to see that while he condemned the selling of indulgences for less than admirable causes, he did not quibble about the efficacy of indulgences.
His main concern seemed to be that some people were merely handing money over to the church and then ignoring the need for true repentance and true penance. IOW, he was worried that this corrupt, off-hand selling of indulgences was leading some souls to potentially lose Heaven through complacency.
Many years ago, I read three biographies of Martin Luther, one by a Catholic, one by a Lutheran, and one by a secular historian. I may have this 100% wrong, but my big take away was that he didn’t intend to create a new religion. It seems to me that Protestantism only happened because the Bishop of Rome had abused his spiritual authority in a bid to be the de facto Emperor of Europe.
The German princes were fed up with being threatened by excommunication and interdiction and jumped on Luther’s ideas, because they provided the theological means to neutralize the power of the Vatican. If they hadn’t elevated Luther into an anti-Catholic superstar, I think Father Martin would’ve been one more priest calling for needed reforms.