A subtle indication of the importance of exit velocity is that instead of one measurement for it, on-line there are many measurements of exit velocity (maximum, average, average adjusted (for ballpark), and average of the softest/hardest half of balls in play).
A second indication of the importance of exit velocity is that someone built a model to determine expected exit velocity and compare expected exit velocity with actual exit velocity.
A third indication of the importance of exit velocity is that it is a big part in determining something widely important - expected batting statistics (xBA, xSLG, and xwOBA).