>>105961616
When the original JPG quality is really high lossy to lossy is fine. Similar to how most people won't store a 20-40 Mbps blu-ray but a smaller 5-10 Mbps H264 rip.

On the web it's a huge gamble whether the JPG in question is of close-to-lossless quality without pixel peeping and whatnot.

Things like waifu2x can recover original images somewhat but it can also cause unwanted hallucinations so that's not going to be widely used anytime soon.