Not gonna answer your other points since they are A) off-topic (I even said "this question is not in the scope of this thread" and you went and answered it anyway) and full of straw-man (nowhere did I say anything about "real music" or "originality") and not worth the retort.
Because if you're a computer arranger/orchestrator (and are trained to know how to write music) instead of just a home producer, Grosso literally disables you from doing what it is you specialize in doing. It's a waste of money because it has no pertinence to what you do.
To clarify, for you, an arranger's job is similar to that of orchestrator, but also has the ability to make musical decisions like changing chords, melodies, forms, etc. instead of only pure aesthetic decisions (like choosing when your woodwinds and which ones will do a fluttery thing). The term composer used to mean an arranger who additionally generates his own musical ideas instead of recycling other ones, but nowadays it just means anyone with a computer, some production skill, and some concept of major and minor scales.
That being said, in the case you're an arranger, orchestrator, and/or the more traditional kind of composer, Grosso limits your ability to take advantage of your skillsets (individual control over instruments, dynamics, voicings, etc.). If you're none of those things and you're the kind of composer who gets music out of his machine no matter the methods, then Grosso is probably better for you. (As I said in the last post, so I essentially repeated myself to answer your question). Not everyone writes music the same, so Grosso's usefulness depends on the person. I'm not sure how much more clear I can make that.
Moving away from general advice and more specifically targeting this to someone like you, the easiest, cheapest, and most autonomous solution possible is more worth the money for you. Be careful, though, because that road is leading to being out of work, since people are making strides in computer generated music and not too far in the future this kind of generic recycling is something you won't need to pay humans to do anymore. (We've already created a categorized database of phrases, just make a system that'll piece them together. It's not as challenging as you might think.) And the more comprehensive we make accessing the phrases, the easier game devs can directly just plop them into their game without the need of a specialized "music guy".
tl;dr Some people like control. Grosso has none. It's not about originality or integrity, it's about preferred work style.