You may be falsely assuming that possession requires both hands on the ball. Seattle receiver clearly has his hand on the ball which is enough to be called another possession.
If a receiver catches ball entirely with just one hand is brought down to the ground by the defender, does that mean the receiver had no possession? So long as the ball does not touch the ground, it is a possession, one handed or two handed.
Look I understand you are a Steelers fan trying to work out frustrations from Super Bowl 45, but look at that photo. I’m not sure Tate’s “hand” is even on the ball. Looks like it is wrapped around Jennings neck.
No person in their right mind calls that a TD or thinks Tate had “possession” for the “tie to the offense” rule to come into play. Maybe Politifact rules it a TD, but that’s it.