Stepping back a bit, whilst this is not exactly comforting, I think a lot of what is driving China and Russia's expansion plans is their demographic cliff-edge.
Russia has a lower fertility rate (1.42) than the UK, alongside a disastrous war and 1.3 million people leaving Russia to avoid conscription (BBC stats from 2023). By the 2040's, approximately a third of all Russians will be pensioners. It's not surprising that Russia are stealing Ukrainian children and one of the reasons for the war was to artificially boost the workforce through annexation.
China's got the same problem - it might even be worse as it's widely acknowledged that the Chinese authorities are massaging the birthrate figures. The official TFR is 1.18 and 21% of their population are already pensioners. By 2040, they will be supporting 400 million elderly people - almost the same as the entire EU.
If Xi or Putin want more territory, they need to do it now. They are not going to have the money or manpower in a decade's time. Even if they refuse to pay pensions and order all the young people to the front, they will not have the same social logistics to support a war effort.
The good news is that if Europe can get its act together, it will be in a strong place. Few people migrate to Russia or China compared to Europe, and we've got the chance to put strong supply chains in place. It would not surprise me if Ukraine emerged as a weapons manufacturing hub, in the same way Israel and South Korea have. I am pissed off that it's taken an extra three years for European leaders to wake up and realise they need to fund defence away from the USA. It's about time they realised that American interests do not align with theirs and are unlikely to do so for the next decade.
The USA might be annoyed about underwriting NATO, but it's also had a lot of political soft power over Europe as a result. That's going to shrink if they get their wish and Europe does increase defence spending.