Not sure if he'd really bench Giroud. Gomez is mostly a poacher, that will have most of the game happen around him. I think there's a fair chance that we'd trade overall playing fluency for better chance conversion. Not that I'm trying to hold Giroud to a high standard here, but if we were to get more out of our other positions I'd still pick him.
As a pure plan B Gomez would probably be a success though, but that comes down to his willingness of actually wanting to sit on the bench most of the time.