In terms of video games, it is. Especially when you (falsely) claim that JRPG's are "huge" outside of Japan. And considering Final Fantasy XIII (both versions) sold well over 2 million in North America, 100K is nothing. 100K is very low in video games, and that is the BEST selling entry in the series (that means every other entry did even worse). I have no doubt it made Atlus money since they specialize in profiting from game with low sales numbers, but it's still niche.
Post the numbers for Persona 4 Golden and then you can speak.
Since the numbers we know show you are wrong, it seems like you would need to find numbers to prove that P4G is not niche like EVERY other game in the series. Even if you trust VG Chartz (which you shouldn't), it doesn't look very good as VG Chartz thinks the game has only sold 470K worlwide (with the majority of those being in Japan).