This observation isn’t new and it has even been scientifically proven. The principle is, when you think about it, very logical… A “diet” soda added to alcohol will contain fewer calories than a more sugary cocktail, your body will take less time to break them down, so the alcohol will be absorbed more rapidly… And to prove it, the famous Dr Karl has done a demonstration with the “Shoey” technique, which involves drinking using your shoe (or your neighbour’s?) as a goblet…
https://www.ladbible.com/news/latest-dr-karl-says-drinking-alcohol-with-diet-soft-drink-gets-you-drunker-20210201