Thank you for the question.
As you mentioned, two choices were provided by the Supreme Court of Canada, and Parliament made a decision about the choice to take.
The thing with the stand-alone offence, the option you just talked about, is that it would actually be something like a stand-alone offence for dangerous intoxication, for example. The thing with that is that the person would not actually be convicted of the underlying offence of violence, such as sexual assault or assault. They would instead be convicted of dangerous intoxication.
Concerns were expressed when this issue was raised back when the initial provision was drafted in 1995 that this would be like a drunkenness discount because the person might not have the same stigma or might not get the same range of sentencing that they would if they were charged with the underlying offence of sexual assault.
The other issue with the stand-alone offence is that only the accused is going to have possession of the evidence that goes to their intoxication, meaning the substances they consumed, so it would be very difficult for the Crown to prove dangerous intoxication because the Crown wouldn't necessarily have possession of that evidence.