shame most people who implement it don't agree

I partially disagree, GI is easy to do most of the time with baked lighting, but reflections (especially more diffuse reflections) are hard unless you have very simple environments or tons of gpu resources to spend on rendering alternate camera angles. Even the more modern rasterized reflection techniques such as parallax corrected cubemaps or screen space reflections break easily if you look at them wrong. Raytraced global illumination and soft shadows are still great though, but are more easy to get around with regular rendering in most games where the environments are very static.