Speaking as someone who had a very high dependency on alcohol (borderline alcoholic) who drank daily, and in great quantities - yes, that is a huge amount.
Alcohol has a vicious hold on people, and with the right "rules" that are placed ("I only drink after 6pm" or "I don't drink on a Monday") it can appear that the "issue" is in hand. It's not. Alcoholism is an addiction and because it is legal to buy and consume alcohol, it is very easy to be lulled into the belief that it's controllable.
Alcoholism or dependency on alcohol can happen for so many reasons and I'm not here to speculate on how, why, where and when. Those can be addressed in due time -the first and most important step is getting your husband to accept or admit that he drinks a lot - probably too much. He may be an alcoholic - he may not; it depends entirely on how he sees it.
It's a bloody hard journey. My dependency stopped when I was placed on tablets that made it impossible to drink like I did, and six months later I barely drank at all. I still have the occasional drink; I never had counselling or therapy for it and I simply do not find alcohol remotely interesting that much anymore. I was fortunate in that I tapered off gradually so didn't have withdrawal symptoms, but if you husband does seek help for excessive drinking, there is every likelihood that it will be painful - both physically and mentally.
The greatest thing you can do is not to accuse or assume, but just simply stand strong with your husband in battling alcohol together.