Maximum ST damage possible

keep in mind that for the premise of this thread, you are at the damage cap.
Whatever amount of +damage a combination is usually able to bring to the table is irrelevant.
What is relevant is your AT's damage cap, base damage, -resists effects, procs and whatever passive damage you can bring to the table (damage Auras, pets etc).

With that in mind, a Corruptor's higher damage cap, higher AT modifier and scourge are going to easily beat the extra debuffs a Defender can bring to the table. The higher damage cap alone should be enough to make the difference.

I gotta say, this is actually a really interesting thread. (Aside from the minor pee-pee contests)....

Some things really surprised me, like 'Crab'? Seriously? Never would have thought of that AT being a top damage dealer in anything but AoE's potentially? (I played one to mid 30's way back when they were the new black).

I am surprised I haven't heard more of my own favourite: Dark Melee/Shield Defense. The combination of the two is just fantastic. Shield picks up for Dark Melee's lack of AoE. I realize this is a tad off topic, but still the single target damage potential is very, very high.

This thread has given me some ideas of potential builds that I never thought of. Which is really great because after so many years, you can feel like you've tried everything. And obviously that isn't really true!

Some great ideas in here.

A Sonic Resonance Mastermind, maybe? Pair it with whatever pets do the most DPS.

If you're at the damage cap then /fire on a melee character for Fiery Embrace is going to go a long way towards helping out. Are you able to look at what kind of debuffs a class can do prior to the attack?

Well I'd be lying if I said I wasn't tempted to pull my old crab out of hiding!

I haven't played him in eons... but you may have convinced me to look at your build and consider it!

Here is the fire dom that is the highest damage dealer I know of:

The -resist in the Interface isn't all that...the always in effect +dmg would be better, with the -resist likely always being in effect anways as the secondary would be the way for more damage I would think.

I think it's already clear to the Arcana's of the forums, but it may be helpful to clarify that we're talking specifically about sustained average damage to a single target over a long period of time.

Technically speaking, the maximum damage possible is probably a Scrapper. That's because it is possible, but unlikely, for the Scrapper to get a critical hit on every attack. This is very unlikely in a long fight. But in a fight where two crits could kill a target, it happens about once every 100 enemies.

Corruptor Scourge is also extremely difficult to place an objective value on outside of regular fights. A lot of this is because the meaning of overkill damage is difficult to evaluate. Strictly speaking, Scourge only adds extra damage if the enemy is killed because Scourge damage contributed. This will happen any time the enemy either 1) takes some amount of Scourge damage and survives it or 2) takes some amount of normal damage and survives that, but is killed by the tacked on Scourge damage.

Sometimes the statement about Scourge above is used to show that Scourge isn't very good; in fact, what it really shows is that "damage values" themselves are not the only measurement in play. Another measurement, that doesn't get a lot of attention from what I can see, is how many animation casts it costs to down the enemy. This is roughly related to DPA but is not exactly the same thing, because DPA is a measure of a steady stream of damage. Equally as important are the whole power casts you bypass if an enemy dies before the next attack. It's also very difficult to measure because it goes completely against the idea of "attack chains"; the best power to cast on enemy that is near death is the one that kills it and sacrifices the least. In some cases this may actually mean having an additional power that is never part of your "chain" and is used strictly as an executioners button. Two kinds of powers that work exactly like this but are rarely called out as such are damage auras and high damage pets, who aren't just useful for the added damage but also for the subtracted power animation investment if used in that way.

That isn't to say that what's been measured elsewhere in this thread isn't useful information. It's just part of the picture.