Considering that Tropical Freeze has sold similar numbers to most Metroid titles, I don't think they really made that big of a mistake.
Metroid II, Super Metroid, Metroid Fusion, Metroid Prime 2, Metroid Prime 3, Metroid: Other M all sold between 1.3-1.8 million and Tropical Freeze is currently at 1.35 million and slowly but surely growing, it will likely do 1.5+ million.
When the herd loses its way, the shepard must kill the bull that leads them astray.