I have a qualm with that statement, I think. Do you have anything to back that up? It doesn't make logical sense to say that "If I have four programmers and they give me nine megawarbles of productivity, and I add a fifth programmer who can only create one megawarble of productivity, I will have a team that only generates eight megawarbles of productivity."
Too often, programmers are drawn into this romantic idea of being a 10x programmer, but I can honestly say that, in my experience, there are more 10x programmers out there than there are 10x programming problems. The IT world needs more data janitors than it needs data scientists.