Again, the game IS the best selling PS4 game released so far BUT Final Fantasy XIII was also the best selling game on the PS3 with a similar install base and still sold double of what XV is doing and it seems that S-E over shipped the hell out of the game and since Final Fantasy is a very front loaded franchise there is a high chance that the game is going to end up in the bomba bins soon
Globally we know that the game is doing more or less flat compared to XIII in UK and we are still waiting for USA numbers to see if the west and asia will make up for the difference.
EDIT: It's not a "biggest bomba" or a "unprecedented success", is more like