When I was thinking "short", I was thinking under 5'8", regardless of gender. Of course, not many ATP players fit that description.
In any case, I never thought of Michael Chang as having a "big" backhand, "big" as in "powerful."
I agree with Limpin here. Good technique should overcome most problems.
However, strong arms can still help, especially when bailing you out of an awkward position. Strength is good, I'm just saying it's not necessary
for a good 1hbh.
Oh, another shortie 1-hander (retired 2007), Anna Smashnova, 5'2", Extreme Eastern backhand grip. Peaked at 15th. Unfortunately, no clean footage of her playing. Here's one though:
Of course we don't know these hypotheticals with certainty. But if you had to bet money on which one would have the least powerful 2hbh, which would it be?
Even you said "it depends on strength," and you also agree that smaller women typically have less strength than larger women. So if that's all we have to go on, the best bet sounds like Henin having the weakest 2hbh, no?
In addition, I wonder if height itself is at least as important as strength. A taller person hits balls that are relatively lower and therefore can more comfortably generate topspin with pace. That same shot will be higher for a short person, and a 1hbh with an extreme grip can generate a lot of topspin with pace, even on high balls, without needing much strength.