Second tier. Middle tier. Neither term is particularly flattering. Both inherently suggest the existence of a first tier or a top tier, which in turn suggest that the distinction between the two tiers is one of quality. And with the ‘third’ tier cornering the ‘specialist’ tag, that one’s out of the question, too.
Perhaps it’s a semantic point, because although the border between second and third (or middle and bottom) tier may be a bit blurry, most people on either side of the client consultant divide instinctively understand who the top tier are. Write down your list and see if it looks something like this: