There were two speedsters on Earth 2.
Zoom was faster than Jay.
Zoom defeated jay constantly.
There was no question that Zoom was the best.
Then comes the breach.
And Barry.
Barry is slower than Zoom and Jay is powerless.
Zoom is the best.
So why is he picking on the silver medalist?
Because people who don't know any better keep calling Barry the fastest man alive? The thing about wanting to be the best is that it's not worth anything if it isn't openly acknowledged...
But, yeah, the whole thing is still kind of unclear. Zoom at this point is still 100% in the cliched bad guy territory - all bite, no explanation.