Shouldn't we be comparing Lallana to Allen and Coutinho, rather than Henderson?
Lallana, Allen and Coutinho all have the same issue when they play in midfield rather than attack. It means whoever is the left sided attacker needs to stay wide and follow the other team's full back. Sterling for example if he is wide can track the run in a straight line, but if he fucks around infield there is no way that Lallana can track the run by running faster in the longer diagonal line to catch up.
On the opposite side Suso can fuck around and come inside because if their left back decides to get brave Henderson has the legs to get across all game long. Eventually their left back will give up, and Suso can then go wide and take on the broken shadow of what used to be a player.