Well let's not forget BOTW was a launch title, many people didn't see Switch itself doing well at all until after launch. We just came off the absolutely terrible January switch presentation. Paid Online? Weaker specs than rumoured? More expensive than rumoured? Mario Kart isn't a launch title? WTF is 1-2-Switch? There's nothing but Zelda?
There were many reasons to question the Switch's prospects, and if the hardware wasn't going to do very well then BOTW wasn't going to be smashing any records. There were also reasons to question BOTW before reviews started rolling in. It looked empty, it was a big divergence for the series and it was Nintendo's first real go at an open world game. It could have easily turned out to have many problems.
That's true, although even if the Switch say only sold 32 million units lifetime, BOTW would still most likely be the single biggest Zelda ever. The only difference is that now we can say that even when including remasters or ports like Zelda Ocarina of Time 3D