Stereotypes are always wrong. Not just in the "You might be a bad person for having them" sense, either.
At the heart of most stereotypes is, or was, a grain of truth. Usually exactly one, and often blown out of proportion across centuries, but entirely spurious stereotypes are extremely rare. Maybe Andalusis were hard drinkers next to other Muslims of the time; maybe Gascons really are hot-blooded big talkers; maybe the French have had mixed results in the last 200 years of European wars. All of that is completely beside the point.
People are not manifestations of Platonic Forms, and stereotypes aren't essential features of us. Stereotypes are contingent; they arise in history - and history is (amongst other things) not what we're writing here. After the Point of Divergence, you have no obligation to keep your ATL convergent, and the more it changes, the more those stereotypes are going to get butterflied away.
For two examples:
- Imagine a Francewank where Napoleon wins the War of the Fourth Coalition and annexes Russia into his empire. Or an ATL where France mobilizes in response to the Rhine annexation, stopping the rise of the Third Reich in its tracks. Or an ATL where Nazi Germany annexes France outright rather than setting up the Vichy Government in its place. What do people think of the French? In that first timeline, they're expansionist and unstoppable. In the second, they're the policeman of Europe, putting an upstart Germany back in its place. In the third, France is the western Poland: overrun swiftly, but it went down fighting, and everybody was in the resistance. In none of these worlds would anybody call them cheese-eating surrender monkeys.
- Imagine an ATL where, in 1924, Lenin's Testament is circulated in its unexpurgated form, ending Stalin's career and (let's say) leading to Bukharin as a Soviet dictator. What would Soviet Russia be, if it wasn't Stalinist? "Just as despotic as the Tsar," probably, but not worse; autocracy and totalitarianism are very different things. It'd still be an ideological threat to other great powers - "red menace" would come up, and maybe "evil empire" too - but in Bukharinist Russia, would television watch you?