I think it would first be incumbent on proving that the middle class in France disappeared before the Revolution-- or that the income gap between rich and poor had widened, which isn't necessarily the same thing-- and I do not think I would agree that either of those things happened.

Strictly speaking about classes, what was far more of a problem with France's system pre-Revolution wasn't that there wasn't a middle class, but that those in the middle and upper middle class were excluded from participating in government on the basis that most of those jobs and opportunities were reserved for the nobility, OR those rich enough to buy their way into the nobility who I would consider the 'elite' (non-nobles whose wealth rivalled that of those in the noble classes).

The common idea that the French Revolution was about starving peasants rising up to bring down the rich is a vast oversimplification and incorrectly identifies the main movers of the Revolution. Those who truly started and carried the Revolution through it's early years weren't the poor, but were a group that Alexis de Toqueville dubbed, "The Notables". This group consisted of middle and upper middle class men, along with liberal nobles, who held the same values (usually based on Enlightenment philosophy) and believed in reforming and improving government. This group was far from the 'starving masses' of either the sans-culottes workers or sharecropping peasants. They were generally well off, and had at least enough money to comfortably live. Some were shopkeepers and artisans on the low end, some were wealthy merchants and landholders on the high end, and most were lawyers, doctors, and other men of legal or bureaucratic positions that held a middle ground money-wise.

Now that isn't to take away from the fact that the lower classes were vital in moving the Revolution along, and their calls for social equality (and their willingness to fight to get it) absolutely was a key part of the Revolution. But for the sake of you question we would really need to prove that, on the eve of the Revolution, the rich and gotten richer, the poor had gotten poorer, and the gulf left a vortex in the middle that flung men into either camp, lessening the steady middle class. Demographics questions like this can always be tricky to avoid anachronisms, but I think we can certainly see a strong, arguably growing 'middle' class in France throughout the 1780s, and indeed many men who would be involved in politics during the Revolution (whether on a national level, which requited a bit more money to live off, or on a local level, where we might see more lower middle class) were firmly of a middle class stock.

So I think whomever was attempting to make this point could not use the French Revolution as an example, unless they are able to find a way to prove the disappearance of a middle class. For what it's worth, you might be interested in John Lewis Gaddis's, The Landscape of History. It's fairly short, and covers how Historians attempt to answer questions such as these. He discusses the notion of attempting to use history to predict the future, and why using models like "the middle class disappearing foretells a revolution" often go wrong. Historical events, even ones that seem similar, are based upon such a wonderful interesting and diverse set of variables that it's truly difficult to find any sort of grand formula for such questions as "what predicts a revolution".

I hope that helps! Please feel free to let me know if you have any more questions!