Whiskey, vodka and other “spirits” are generally 80 proof or ~40% alcohol. A 1 ounce “shot” or “drink” is .4 ounces of ethyl alcohol. Four drinks a day are the equivalent of 2 ounces of ethyl alcohol and is considered heavy drinking. Same principle applies to wine and beer (wine generally 12% alcohol and most beer ~ 4-5% alcohol.. You have to measure what you drink. Heavy is bad and takes its toll. Bad on the liver and brain and can also be associated with many cancers.
Your math is a little off, because a shot everywhere in the civilized world is 1.5 oz, not 1 oz. So 40% alcohol by volume x 1.5 oz = 0.6 oz of alcohol per drink, so 1.5 oz of alcohol per day is 2 and 1/2 half drinks a day, not 4 drinks a day.
4 drinks a day (unless you are chugging them in quick succession) is still probably not “heavy drinking” but at least it’s in the ballpark. 2 and 1/2 drinks a day is not.