MGSV sells on par with previous entries, but is now the best the console has to offer in terms of sales by a country mile. That wasn't the case even on the PS3. How is it not sad?
MGS 4 was the best selling PS3 game until Final Fantasy 13 or Resident Evil 5 came out so it's the same exact situation. Unless you mean MGS V is the highest any game will sell in Japan for the entirety of the generation, which of course is wrong.