Oatly has never pretended sugar is good for you, it's listed on the box, we all see it. And I don't think they should be put on blast for their use of canola oil of all things..and by the way nobody is drinking it because of the health benefits of that.
The most effective thing they did from a marketing standpoint was an anti-dairy campaign. Their biggest achievement is making people go "Yea... cow's milk is kinda weird, why wouldn't I drink an alternative that tastes just like it".
Coke, cigarettes, sugar campaigns -- They sold you on this idea that life can be more amazing if you just use this product.
Oatly did something different. They said "Hey your life can be about the same as it is now, enjoying dope milk, but without drinking cow's milk like a weirdo". And it worked.