I wouldn’t rely on the texture viewer preview too much, as it seems to display things in sRGB space regardless of the settings - that’s where the color differences came from too, not from compression. My mistake.
The material editor shows things as they should appear in game since it’s using the same shaders, and if the texture had sRGB disabled in the image in your original question then that actually appears to be working as intended.
Did you try comparing the original file to how it looks in the material editor with sRGB enabled? If it still doesn’t look right then I’d suggest setting a vector to the correct color value and seeing if that’s displayed similarly.