Without a doubt, the NFL is not Watson's ally in this situation. By appealing, the league is rejecting the six games imposed by Robinson in favour of a harsher penalty.
There were rumours that the league might hand Watson a 12-game punishment as a concession. He might very well receive a full season's suspension from the NFL.
Despite the NFLPA's unavoidable opposition, the league should be able to impose the punishment it sees fit because Robinson agreed with the NFL on the breach of the personal conduct standard.