It's really strange to me that a lossy compressed format could be called "raw". Does that just mean that it hasn't been e.g. gamma-corrected before the compression was applied? (Is it even a good idea to do lossy compression before such correction?)

All raw means is scene-referred data. The idea that somehow raw means "raw" data from the sensor is an often repeated idea, but unfortunately is completely nonsense. Modern sensors do on-chip noise reduction, they can be programmed to give data in all kind of formats and with different processing done to it. The same sensor used in different cameras can have different ISO. The same sensor used in different cameras can produce different RAW files even at the same ISO. Not just in the sense of a different file format, in the sense of different data in the file, from the exact same sensor, but programmed differently.