Super Smash Bros. Ultimate recently became the best-selling fighting game in history, a record previously held by Street Fighter II. According to the folks at Japanese Nintendo, “[Masahiro] Sakurai says that Smash is considered an action game in Japan. Even though it has suprassed SFII in sales, he still considers Capcom’s classic to be the king of fighting games still. Sakurai says a fighting game may become stale once mastered, hence why the series is designed closer to a party game.”
Source: Japanese Nintendo