Today, while researching gaming books, I came across a picture of Phantasy Star II appearing in one place I would have never expected to see it: the Nintendo offices circa 1989.
In a translation of a children's book about the creation of Super Mario Bros. 3, there are some pictures of the developers at work. If you scroll down to the fifth set of pictures on that page, you can see Shigeru Miyamoto and Takashi Tezuka, two of the guys who worked on a lot of Nintendo's big titles like Mario and Zelda, hard at work on designing a level. Tucked away in the corner of Tezuka's desk, above Miyamoto's back, there are a few Mega Drive games! The picture is blurry, so it's a little hard to make them out, but based on the colors, one of those games is Phantasy Star II.
So, there you go. When PSII came out, even some of the most important guys at Nintendo were playing it in the office.