Avira, there is also “v’asita hatov v’hashar”. This, apparently, is behind the Be’er haGola’s famous statement. The Netziv says in his introduction to Sefer Bereisheet that the Avot werecalled yesharim because of this.
You are wrong about Rav Hirsch. He believed in studying German culture as well as science and math. This was Torah im derech eretz. In his commentary on Pirkei Avot he writes
“Derech Eretz includes everything that results from the fact that man’s existence, mission and social life are conducted on Earth, using earthly means and conditions. Therefore this term especially describes ways of earning a livelihood and maintaining the social order. It also includes the customs and considerations of etiquette that the social order generates as well as everything concerning humanistic and civil education.”