Without looking at all the effects together, the comparison product (alcohol?), and the actual change in risk it’s as likely to confuse as inform.
Ever since cannabis use has become normalized there has been a vigorous debate about its long term safety and the issue is far from settled. This study is another data point that we as individuals can use to make decisions about cannabis use.
You are right that in practices we can't just look at cannabis use in isolation from the rest of a persons lifestyle. However, science almost never starts with a comprehensive analysis. Instead it starts with smaller targeted studies that are then used to build the comprehensive arguments.
So while yes I it would be more useful know the risk of cannabis use relative to drinking alcohol, consumer sugar, lack of exercise, etc... this data point in an of it self is still useful.
I think HN crowd is more likely to read one article out-of-context and over-extrapolate. In this case, there's no article even linked, just an abstract, so anybody jumping to conclusions from this isn't being very HN.
Somebody who was really HN would read the whole article, see what doses, what % risk change, what age, see what other studies say, etc.