While I don’t believe that rape culture can be turned around solely with harsher sentences, harsher “we mean business” sentences do need to be part of the solution.
After all, drunk driving was a problem that was just winked at in this country for years. When we got serious about penalties for drunk driving, it caused a shift in thinking about getting behind the wheel after having a few. But education about alcohol consumption and what it does has helped as well.
Culture of any kind is difficult to change. It always takes a number of approaches applied simultaneously to budge it.