I experienced this many times.
I know how the performance works.
But performance dropping after winning because opponent was low rated is ABSURD.
Well, no, as anyway you will always be better ranked with two victories than with only one
No. Consider this:
In atomic, I'm rated 2150.
First game: 1300 opponent . Win. Performance: 1800
Second game: 1200 opponent. Win. Performance becomes 1750. What ? This is absurd.
And ? Performance stays only a way to rank people with the same number of points. Consider it only as an opponent average modified by one's winning rate. You would be better ranked after your second game than after the first one.
I care about my performance.
Glicko 2 definitely has a few faults in the way it rewards points. I think much of it has to do with ease of programming and system maintenance rather than "fairness", which can be subjective in attempts to please everyone. There is no single rating system that pleases everyone, if there was, it would be universally used.
Not rating. We are talking about performance.