evil options are often embarrassingly contrived and make no real actual sense

I totally agree with this. It always seems developers put it in because they feel they have to.

this polarised system totally breaks as soon as your evil character would be advantaged by taking "heroic" dialogue options

This is why good and evil in video games is essentially broken these days. Plus as the link from my previous post explains, there is no consequences for doing the heroic or evil choices. That is it does not matter which is chosen except for the immediate reward. This hits on a topic that has kind of disappointed me about the game industry, most games lack real depth.