Did you miss the post earlier that shows Nintendo has sold 85-115 million every generation excluding Wii/DS?
So 80M is below the lower bound of that interval (which already ignores the most successful generation for Nintendo) and you would consider it a success?
when you factor in the overlap of people who purchase both a handheld & home console each generation and now only need to buy a single device than yes 80 million is a good number.
regardless i dont consider something a success based solely on hardware numbers things like software sales & profit have to be taken into account as well. if Nintendo sells 80 million units of Switch over the course of 5-6 years, sells a few hundred million units of 1st party software, a few hundred million units of 3rd party software and makes the company a few billion dollars in profit than yes it would undeniably be a success.