Mr. Churchill was himself fairly short (and "portly"), and the short-barreled gun worked out well for him, and with the shooting style he developed to go along with it. But there was certainly a "gimmick" factor as well. Most of those guns were sold after WWI, and because so many young English gentlemen never returned from the war, there was a larger than normal inventory of used guns on the market, most--following the tastes of the first couple decades of the 20th century--having either 28 or 30" barrels. In that "between the wars" period, Brit makers were trying different things to attract buyers, like the XXV, the 2" 12, the 12/20, etc.
I'm certainly no more than average height, and I've owned a couple Spanish copies of the XXV. Neither one worked out very well at all. But for some people, they certainly do.
I never had a problem shooting a real Churchill XXV, in fact...I really like them. I sold my Regal grade, but I plan on owning another one...next time I will move up to Premier grade when funds permit.