I think a combo of both is necessary. A couple things come to mind. First, we really need to identify where on the force-velocity spectrum we are talking about. Are we talking about very fast movements like sprinting and throwing or are we talking about maximizing power output from a purely mechanical standpoint. My answer is largely the same but the details of my response would vary depending on the answer to this question. Regardless, it is often beneficial to work at points other than the specific target area on the force-velocity spectrum because there is a considerable carryover affect. As such, using high force, lower velocity movements (like squats) can help with power development even though they are in a different location on the force-velocity spectrum. Such movements focus on developing the force component of power. Similarly using very high speed but lower force generating movements can be beneficial because they place a training emphasis on the speed component of power.
There is plenty of research to back up this viewpoint. The Olympic lifts (especially the snatch and the jerk) have been shown to be the most powerful movement in the sporting world so performing OLs and similar exercises can be beneficial to increase power output via training specificity. Also, numerous studies have indicated that when training to increase vertical jumping ability that a combined strength and plyo approach is more beneficial than either one alone.