Concerning the diffuse:
Is there a reason why you are using a linear color 16 bit texture for diffuse? You seem to have SRGB unchecked for the diffuse texture which is turning it to “Linear color” that adjusts the gamma internally, this is why you are re-gamma correcting it by 2.2 to get the correct colors.
I imported your jpg texture into unreal, it came in looking fine with the default SRGB checked for diffuse.
- In general though I found using 8 bits across the board for all textures to be enough for almost all scenarios save a few.