The Yak is a good plane.  It can outrun most of the planes that can outturn it, and it can outturn many of the planes that can catch it.  Also, there are a lot of planes that it can both outrun (or catch) and outturn.
I think the Yak might also be one of those planes that's hard to see.  I can be 300-400 back with a fine firing position, but the Yak can be against a background that makes it very hard for me to see if it is just jinking a little.