No, optimum just tries to balance between distance vs time rather than completely basing route on one or the other.
I have also purchased the traffic add-on and it has proven very useful in unexpected ways. I've even had it take me /farther/ out of my way to put me on a highway route it calculated would get me there faster, based on traffic conditions in addition to my "optimum" setting. And it actually was faster than it would normally take me to sit in traffic on the usual route. I was pleasantly surprised. Now I tend to trust it's judgement more.
But even if you don't, you can access the list of traffic incidents and it offers a means for you to elect to ignore or force it to route around different situations. I've done this as well, just to try it (avoid problematic interchanges) and it performed admirably.
I've noticed in the 1.4 update that it's a bit more hands-off in the default display than 1.3 was. that is, it doesn't always show the traffic icon in the top left. But when it's there you can tap it to get at the traffic incident list. It displays an icon in the lower left, too, to indicate that the route is being adjusted for traffic issues. And even if the button isn't displayed, you can get to the traffic incident list via the Options button in the map display.