The claim is that Oatly is not a good substitute for milk, and that cow milk is perfectly fine to drink for a good percentage of people, which I judge the article demonstrated satisfactorily.
You can of course say you don't want to (or can't) drink milk for a very long list of absolutely fine reasons. The solution then is to just not drink milk, not substitute it with oat-canola slurry. Or you could reduce your consumption to the point where its price can go up (as more of a luxury product) and allow manufacturers to treat animals ethically. Or buy it from responsible farms.
You can also make the point here that there is a great number of people who, when faced with the choice of "drink less milk" vs "continue cow abuse", will pick the latter because they like drinking milk more than they care about cows (which are bred specifically for human consumption). In that case you could argue that substituting Oatly for milk will make the world better, because it lets them lower their milk consumption without requiring sacrifice on their part. The thing that worries me here are second order effects - if Oatly is indeed not very healthy (which it sounds like it isn't, at least compared to regular milk), then these people will then suffer lowered cognition and worse health, leading to them making less than ideal choices in democratic elections, and putting more strain on the health system.
Again - there are good critiques that can be leveraged against our current farming practices regarding milk production and more, but I don't see the solution being switching to synthetic alternatives with potentially harmful effects that marketing makes their best to prevent you from knowing. Just go without and advocate for change.