According to JJB, the administrator of WarezNX which is a Discord channel dedicated to Switch piracy, this level of leaks is somewhat unprecedented. Leaks and pirated copies of games appearing a day or two ahead of the official release is to be expected, but as JJB points out, a good two weeks is a rather huge leak, although given the popularity of the game we can’t say we’re surprised.
It is unclear as to what Nintendo is doing to address these leaks, but unfortunately it’s hard to do much after it has been put out there. Nintendo has systems in place that help deal with piracy, and it has been discovered in the past that modifying one’s Switch console (presumably to enable the running of pirated content) can result in users getting banned.
It is also unclear if this leak could have a negative effect on the game’s release, but judging by how it has smashed various pre-sales records, it seems like it might not have mattered too much.