Thats not just the sales pitch. I experienced it practically and i brought it up as an example.
I don't know where the sweat spot is, but i don't think it is at a 10 person company. I believe its more in the range of 500 or 1000 person company.
That's the sales pitch, sure.
Size scales in reverse order with security. The larger you are, the more difficult it is to make sure all the gaps are sealed - that's why the greatest of empires fall eventually - they get spread across so large a portfolio there are bound to be gaps, which are endlessly exploited, even on users of the large ERP companies.
If products were actually integrated well and deployed well all of what you say would be true. But that's just not the reality - trust me, I've been there. It's bad.