You cannot presume your PH is the best shot in the world, or that he reacts well under pressure.I have seen the best and worst of both.
I agree, the best attitude to have is that of a person hunting on his own.
You also need to strike a balance. Look at some of the DG hunting videos and see hunters with heavy calibre weapons flinch, and generally shoot poorly. A well placed shot with a 375 H&H mag would be infinitely better than half a dozen 470's in the rumen.
M.