Kramer is worth an entry in an atlas of religion not because he was influential, which is disputed, but because his career lays out how the machinery actually worked when it worked at all.
An inquisitor arriving in a town had a commission but no local standing. He needed the cooperation of the secular authorities to arrest and to execute, and he needed the local bishop not to object. Where he got both, prosecutions could run. Where a bishop or a magistrate declined, as at Innsbruck, they stopped. That is why maps of the persecution are so uneven, with slaughter in one territory and almost nothing in the next: what varied was rarely belief and usually jurisdiction. Regions with strong central courts reviewing local verdicts prosecuted far less than regions where a village court could convict and burn without review.
Kramer went on to work in Bohemia and Moravia and died there around 1505, having spent a career pressing an argument that many of his own colleagues would not accept. The reputation that grew around him afterwards, of a man who single-handedly lit Europe, is a nineteenth century picture and it flatters him. The trials came a century after his death, in courts he never sat in, and they had their own local reasons.
None of which softens what the book did once it was in the hands of people who wanted it. Kramer supplied a shape, and a claim of authority, to anyone who later wanted a reason to set procedure aside.