Not quite. Speed is life. But if you want to turn (i.e. in a visual, turning fight), you need to be at corner velocity.
That's generally true, but there are countless other variables at play. Turning fights are brutal absorbers of energy. Once you get to turning really hard speed rapidly bleeds off and maintaining corner velocity is difficult. And thrust vectoring tends to make that worse. This is where sustained turn rate comes into play. How much G can you sustain in a turn without losing altitude. It's very easy (indeed you're almost certain) to find yourself trading altitude for speed in a turning fight. So while the thrust vectoring gives you exceptional control of nose pointing, it comes at the price of speed (or altitude). And (theoretically at least) with HOBS weapons and HMDs, nose pointing is not nearly as critical anymore.