Actually, the problem isn't that modern games "look worse." What's really the issue is that video hosting platforms still only display captures in 1080p resolution at subpar bitrates, and purposefully employ codecs that turn the image smudgy. Therefore, games that are recorded or livestreamed often turn into incoherent messes of blocky pixels and blurred particles, because the output supplied by the host simply cannot keep up with what's happening in-game. It's a problem completely separate from hardware, optimization or anything involving the game's development.