Let me ask you this. If someone suddenly told you you scored 12 points and left it at this would it mean anything? No extra information, no context nothing. Just a number. And that's what DPS meter would be in vacuum. There's really a lot of work that's needed to be done if there's ever going to be serious attempt at using Damage Meter as an improvement tool for players there's a lot of data you actively need provide at moment's notice. What's average damage? How does Player's performance compare to it? What's practically achievable maximum at any stadium if the class progression? How much of that is actively required to clear content at given level and difficulty. Without this data to draw on the Damage Meter isn't different from any random scoring method. Just assigning score among party members without putting it into context doesn't invoke Improvement but may lead to even more toxic interactions even if they wouldn't cross the lines marked by ToS. We're already damn creative at being pricks to one another without breaking it.

Ultimately it's not a bad idea but it's something that would require titanic effort to implement right. Effort that neither Devs or community is willing to put.