I feel the average junior developer’s, or even senior developer’s, for that matter, code was a lot worse than the average SO response, which has now become the baseline for all types of devs, so their code is at worst as bad.
When I look for an answer, I do look to Google and/or stackoverflow, but then I immediately turn to figuring out how to find the "real" answer.
Also, a lot of times, Google's approach to identifying the single answer to your question means it masks any similar question, making it severely handicapped in answering anything difficult. But if it wasn't a difficult question, I wouldn't be asking!
You cannot develop an app, evaluate different solutions, choose an architecture, address performance problems, etc, via StackOverflow. StackOverflow is for specific problems; it can help you sort out some errors, because most of them aren't exactly coding problems.
A senior engineer's job isn't just to make an app compile, so you cannot reach this position just by searching SO.
Even Joel Spolsky (creator of SO) has brought up some negative impacts of StackOverflow (on his old podcast at some point), saying nobody needs to learn anything anymore, just jump into the code and google the error messages.
I'm guilty of this too, I just think it's a shame that Googling is preferable over learning...