Advantage on damage rolls

[Former user]

"Advantage" on damage rolls seems to be unsupported. The intended use for this effect would be if a feature allowed a character to reroll their damage and choose the result, or roll twice and choose the higher result.

I've run a test and there is no statistical difference between having advantage on a damage roll and not. Related features like rerolling damage die results lower than X have their intended effect. I imagine this isn't included because I'm not familiar with any case in core 5e where there is an effect like this, and because there is no good way to currently display this without having a second damage roll displayed.

I imagine this could be supported by having a second damage tally for the alternate roll, in a similar manner to when two damage rolls are made in one attack, but just separating them and not combining their totals, and potentially highlighting the higher result akin to advantage on any other roll.