The Myth of Churchill and Alcohol: a Distortion of the Record (2018)

(2018) I honestly don't know if that matters in this space.

Skimming the article - it sounds like an ideologically-motivated response to some ideologically-motivated (and perceived as hostile) claims about Churchill. So I'd take it with a very big grain of salt, even without the Hillsdale red flag.

Bigger picture - if you read quite a bit of the British Empire's history, then "competent, sane, and sober" can seem like a depressingly rare trio of virtues in its leaders.* Trying to analyze Churchill without the context of his times and social class is simply misguided. Similarly, the period from ~1905 to ~1955 was brutally stressful for British leaders who cared about "their" Empire, and trying to preserve it. Many of those leaders died early, from various combinations of the stress and their chemical coping mechanisms (chain smoking, heavy drinking, etc.).

*And the latter two of those tags are of very limited use, in trying to puzzle out whether or not someone is a passably "good" leader.