Would granite tile work? A compromise? That's all I've got...not an expert and don't want to get hit by collateral damage :)

We're currently remodeling our bathroom and will have a granite tub surround. Our granite guy will not take his final measurements and template the surround until the tub is framed in and sitting in place. (Just the opposite of what your granite fabricator is telling you)

Maybe there is something different about your set-up or maybe your fabricator is inexperienced/inept. Consider calling in a different "granite guy" to see if you get the same story.