They all play in different positions so I'm not sure why they are linked.
Sanogo is far from special but he might prove more valuable to the squad than Jack this season. Even if just as a injury crisis buffer of sorts. We are well stocked everywhere but striker so it makes sense to keep Sanogo as an 'on the fringes' kind of player, as opposed to the others.
I am of the impression that Gnabry is years away from being of value to the wings himself, so why does it bother you if he is no longer available now?
The problem with top level clubs is that they can't really afford to hoard elite youths outside of the starting 11. The players either stagnate through lack of game time, or they get their game time but due to being in development, don't allow their team to operate at full effectiveness.
Damned if you do damned if you don't with youths tbh. Sanogo might surprise us all though.