Anyone who cares about whose bar is the longest is already measuring on their own screen. Not only is the reporter almost always on the top (and conveniently never reports when s/he is below), but displaying the damage done for a fight to the same raid who's on the meter is just pure epeen spill. Asking for a damage meter is just laziness (or, in rare cases, a really crappy computer paired with a log-intensive fight).
Let's not forget that problem of boiling a player down to a single number. All three roles of the holy triad have a complex set of abilities for every encounter.
When judging a player's performance in a raid or dungeon, my first thought is whether the job at hand was done. Did the tank survive and keep adequate threat? Was the party healed enough? Did the enemy mobs die? Was the bare minimum of a job achieved?
Total or overall damage done will include trash numbers, which slants heavily to burst and AoE specializations. "DPS" mode can mislead as well, since a player who has died can often still be seen in the top spots. Effective DPS -- DPS (e), or the DPS that World of Logs uses to rank players -- is damage done over the fight's duration.
Current fight plus Damage Done (not DPS!) tends to be the most effective general meter for DPS players. The caveat is that it is only a very general meter. Healers should look at absorbs as well as direct healing. Total healing includes overhealing. Tanks may be more interested in buff uptimes for their active mitigation as well as looking at the Damage Taken mode.
Damage meters can show times a CC target was broken, but they won't tell you whether the correct target was crowd controlled in the first place. There's an extra addon to both the main damage meters that can count the number of times a player stood in a bad thing, but raiders could have been responding promptly to a wipe call and intentionally stood in something. Interrupts and dispels are counted alongside deaths, but even the death counter has expanded into a "what killed me" log.
But just as the bare minimum doesn't make a great player, playing a little imperfectly doesn't make a terrible one, either. There are more things in guilds and Azeroth, Horatio, than are dreamt of in your damage meter.