Fitzbackup looks like a QB in his 14th year on his 13th team. Anyone expecting even serviceable for 16 games is looking for disappointment.
Fitz is more than serviceable for stretches. He's easily one of the best backups in the league. With the fire and ability that Rosen has displayed, and with this team realistically rebuilding, it doesn't make sense to start Fitz at this point.
If Rosen had been overmatched it would be a different story, but he hasn't been.