It almost looks to me like either the B-pivot spring is broken/disengaged, or the screw has missed the intended resting place on the RD hanger entirely. Did you rotate the derailleur back while bolting it down, so its screw gets behind the stop as intended? Here's a rear view showing how the B-tension screw should rest on the dropout:
If the derailleur's mounted properly, then the spring in the upper pivot should rotate the whole derailleur backwards if you introduce a lot of chain slack by taking the chain off the front chainrings and resting it on the bottom-bracket shell. If it isn't doing that, something's amiss, possibly a broken spring (unusual but possible).