Thankfully, Russia doesn't really have 5th Gen either. Europe has a lot of solid 4+ gen planes: Rafale, Eurofighter, maybe Gripen. And I'm willing to guess that, especially with better trained pilots, these are potentially better than Russia's assortment.
But there remains a question of quantity and determination.
The surviving Russian pilots fly towards the front line at a high altitude until they get close to the suspected range of Ukrainian air defences, drop glide bombs and then turn around. Sometimes the Ukrainians have snuck an air defence unit closer to the front lines without it being detected and the pilots exit the category of surviving Russian pilots.
I'm not sure how applicable this would be to a confrontation with European countries. Russian fighters will get getting lots of flight hours on CAP as well, but not much combat based on reporting. Both sides are keeping everything inside their own AD bubbles.
So far their 5th generation fighter program has been an even worse embarrassement than the T14 Armata.
Their own press photos shows uncovered Philips screws on a supposedly stealth aircraft, and their "loyal wingman" drone used the first opportunity near the frontlines to try to defect.
Sure, but that risk is just something Europe has to eat as punishment for buying F-35 instead of building their own, it doesn't affect the new reality that US aircraft cannot be trusted in wartime.
