I've worked alongside consultants from Accenture, Deloitte, IBM, etc over the years and, while many of them are very competent, I would /never/ engage one of those large system integrators (SIs) on any project I was involved in. There are many excellent individuals working for those companies, but the companies themselves are terrible and you will struggle to get any of the excellent people involved during your implementation. The experts will appear during the early stages of the consulting sales cycle but will be nowhere to be seen during the implementation.
Unfortunately this is the dirty little secret of SAP implementations. Many SAP customers think "I'll pay top dollar and get a good SI" but they end up getting the latest round of juniors doing the implementation. Seen it many a time.
Your comment is a mechanistic explanation of the failure mode, which again, I quite agree with. I worked at PwC for a couple of years; quite corrupt incentive structures and quite a dysfunctional organization because of it.
