You mean a relative potency boost. A flat potency boost is irrelevant if you boost everyone by the same amount. And it does. Change the weighting, change the impact the player has. At the very least, it means that having a tank with good uptime is somewhat important to clearing.

Granted, it is unfortunate that the primary way that we can impact fight outcome at the moment across roles is through dps. But that's why it's not the only thing that needs to change.