Performance analysis is incredibly complex and nuanced. Judging if somebody is performing poorly because they are unskilled or not managed properly or having marital problems is hard. Improving performance is even more difficult because it requires the analysis and a remediation plan.
And I don't know your scale of 'good' programmer either: What do you mean by that? Are you saying you are as good as Linus Torvalds or are you saying you are better than your current peers? I am assuming it is the latter - which probably means zilch in a site like this. Many folks here receive that recognition and over time they come to a conclusion that it doesn't mean much. Which is why you get a lot of naysayers. They aren't doubting you, they are just doubting the general feeling as been there, done that.
Look at this thread, there are several who are very explicitly doubting me in no uncertain terms. Even doubting the idea that I'm good compared to my current peers.
I suggest you reflect on this. It seems to me that you've convinced yourself that you are good at certain things but there isn't really any evidence supporting your beliefs.
When I was younger, I actually used to think like you - that perf evaluation is easy and a good engineer (e.g. me) would be able to evaluate others easily. Over time, I've realized this is an incredibly complex and nuanced issue because everyone's strengths and weaknesses are so very multifaceted. I am more or less convinced that people who think they have all the right answers simply have a lot of blindspots.