Bitrate is a useful indicator. It's the amount of information that is directly linked to maximum quality, there are bounds on what can be compressed by how much

Bitrate is a useful indicator. It's the amount of information that is directly linked to maximum quality, there are bounds on what can be compressed by how much. Fact is, x265 can do 25-33% smaller size than x264 for equivalent visual quality. The higher gain at higher resolutions (2k, 4k) that were not well supported by older codecs anyway. You can refer to Netflix own papers on that. Services doing half the bandwidth have reduced quality. The improvement in codec can only explain half the reduction, the other half is grossly lowering quality (to reduce costs and work with mediocre home connections). That's not necessarily bad for customers, better have a pseudo HD stream than no stream.