I haven't seen it (yet) but I saw a quote from the Director saying that they were not introducing alcoholism (yet) but saving that for a later movie. Stark parties. Stark drinks. But it's not a problem (yet).
If anyone has seen it and can tell me if I'm wrong, I'd appreciate it.
Before Stark’s conversion, he drinks. A lot. Almost every scene has him with a drink in his hand. The very first shot in the movie is his drink.
But you’re right, his partying in general is the problem in this movie. And alcohol is just an element of that.