Trying to understand this comment

I'm trying to understand this comment that I found on Youtube.

ゲームが世紀の大駄作じゃなかったらテイルズないしゲーム界で名曲になってただろうなあ

What I can understand is: if this game wasn't a huge pile of garbage, then without a Tales game, this song would have become a famous song in the world.

Or something close to that...? What does "naishi" mean in this context? Or is it "nashi"? :v

I don’t know the background, and don’t even know what “Tales” refers to, but does this make sense?
- If this game had not turned out to be a flop of the century, then (the song) would have become a famed song either in the world of Tales or in the world of games.

In my translation above, I interpreted this “naishi” to mean “either.. or.”