I can see the argument for Pally + 4x Shaman > 5x Shaman... in some situations.
Cannot see that Pally + 4x Shaman is always better then 5x Shaman.

Take Sam for example.
He already has: 1x Pally and 4x Shammy, as the first group.
In Sam's current non- FTL setup, which would support this group more:
a) 30 additional Shammies; or
b) 25 additional Shammies, and 5 additional Prot Paladins.