This is another subject on which I am by no means an expert, but this question seems to me to involve something of an over–simplification.
Angela Merkel is a Lutheran; in fact her father was a Lutheran pastor. In 2017, the 500th anniverary of Martin Luther's 29 Theses, The Economist described how "Martin Luther has shaped Germany for half a millennium". But statistically, it's not even true to say that Protestantism is predominant in Germany. Most sources, including Wikipedia, put Protestantism slightly behind Catholicism (26.1% and 28.2% respectively, according to Wikipedia.)
The vast majority of German Protestants belong to the Evangelical Church in Germany – a federation of twenty denominations. Wikipedia states that "[m]ost of its members consider themselves Lutherans", but lists its constituent parts as United, Lutheran and Reformed (in that order). The Reformed tradition is essentially Calvinist, while "United" refers to a movement that dates back to 1817 and unites the Lutheran and Reformed denominations.
In conclusion: it does appear that Lutheranism is probably the largest religious denomination in Germany, but it's hardly "predominant" – even amongst the Protestant denominations.
And BTW – it's "Lutheranism", not "Lutherism".
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