You're missing the point.
Do you want paid QA/Testers to spend time on hunting obscure bugs related to a myriad of possible invalid game states, rather than an actual bug? Or worse, hunting obscure bugs related to a myriad of possible invalid game states - AND - tracking down a bug, only happening due to an invalid game state? Its kind of recursive.
Regarding CK2, you have to ask how they do it in their subforum and link their answer here. I have no idea about CK2.
The invalid game state bug is not an obscure one.
Data corruption bugs are very real and serious.
Debugging indeed sucks. Because you never know how faraway you are from fixing the stuff. Sometimes many seemingly unrelated bugs are caused by a single error, so tracking one bug could end up with fixing several others. Other times you thought you just need to fix a bug, only to find it's actually caused by a partial fix of another bug complicated by a few broken workarounds.
Two years ago, about time when I just finished my master's degree, I criticized the EU4 time's decision harshly, for them choosing to band-aid the problem instead of trying to fix the root cause.
But now... with my increased experience... well, I think they made the right decision. The priorities are important. On time delivery of working stuff that's actually stable is indeed more important than fixing a hypothetical "root cause".
However, I am still a bit afraid that this becomes sort of technical debt that grows exponentially and could never be paid off.