Thanks Gryphon.
The lack of deep blacks is on purpose, and a result of PP.
That being said, it is true that the Tamron is less contrasty than, say, any Zeiss I have (25/2, 35/2, 50/2, 135/2). It is probably very good for portraits (1/2 body, or nudes...) in mild tones, but I have yet to test it under such circumstances.