That's my whole point: revolutions are more likely to happen earlier on, because the longer you have capitalism the bigger the middle class gets.
Unless the middle class shrink back like it's happening right now. But before WWI is largely possible for a revolution in Western Europe. You could even argue that this period extend a few years after WWII (or else why the OSS would have fixed the first Italian elections after WWII).
Only if you cherry pick years and countries. If you take the median wage in Europe 15 years ago and now, it would be much higher now.
Actually i only know the figures for the US (and France) but the Median household income (ajusted for inflation) is pretty much stable since the end of the cold war. In France it is has only increased by 10 percent since 1990 and everyone in France knows that the inflation figures a largely underestimated.