Garent

So you never attacked?

If you think that's the full unrealized power of defenders then you have a long way to go. My defender runs in ahead of the rest of the team and does damage fast enough that the enemy mobs drop before I lose too much aggro and before I die. Aid self if necessary, then move on to the next group.

The Achilles heel is limited to one per person. Masterminds can get around this by slotting the proc into their pets since each of them will act as a seperate entity.

The mez resistance cap was -massively- increased with the issue 13 pvp changes. It's now impossible to reach the cap under normal circumstances.

I think that howl is so important in a team situation that it shouldn't be used in an attack chain. It should instead be used every time it's up as long as a more pressing primary power isn't needed. Though I'm of the opinion that things happen so quickly on large teams that it's not possible to get any sort of chain going except on bosses near the end of a fight.

Electric fence is equivalent to a tier 1 blast in terms of damage and recharge, except with a longer animation time, higher endurance cost, and its damage is dealt over time. That means power bolt is better than electric fence. In fact, it barely has a higher DPA than shriek and doesn't have a resistance debuff. Shout is clearly better.

I used debuff duration over animation time. Cycle time at higher levels only affects how often a power can be used in an attack chain, not how useful it is in the chain.

This was actually what -everyone- thought when city of villains first came out. Brutes were tankers/scrappers done right, dominators were blasters done right, corruptors were defenders done right, and stalkers and masterminds were the new guys.
In my opinion, brutes and dominators have very clear advantages over their similar heroic counterparts, but corruptors and defenders are similar to the point that they have nothing to fear from eachother. My first corruptor was actually the worst solo character I've ever had (ice/cold) meanwhile my first character and defender (storm/energy) spent half of his journey to 50 soloing. The reason for this difference is powersets and not archetype mods.
In my opinion though, defenders are better. If I could, I'd give my ice/cold corruptor defender modifiers and inherent. Most of his damage comes from procs, so my damage wouldn't take a very big hit and the more powerful defense buffs would be well worth it.

That's exactly my point. If Achilles' heel is tagged as being resistable, then it can't be the reason for the -20% showing up on an AV.

You answered the question yourself. Howl is inferior single target damage and debuffing.

raw data:
shriek- 30.4 dam, 1s cast, 5s debuff
scream- 47.7 dam, 1.67s cast, 7s debuff
shout- 76.6 dam, 2.67s cast, 10s debuff
screech- 7.23 dam (negligible), 1.5s cast, 12s debuff
howl- 29.3 dam, 2.33s cast, 8s debuff

The two important things to consider are damage per second (damage divided by casting time) and debuffing per second (debuff duration divided by casting time). Damage per second's merit is obvious. Debuffing per second serves as a representation of how effective the powers are at increasing the -res stack. Debuffing per second is actually a really misleading name for this unit, but it's better then calling it Debuff Duration Measured in Seconds Per Second. The results are as follows.

shriek- 30.4 dam/s; 5s debuff/s
scream- 28.6 dam/s; 4.2s debuff/s
shout- 28.7 dam/s; 3.7s debuff/s
screech- 8s debuff/s
howl- 12.6 dam/s; 3.4s debuff/s

As you can see, howl is the worst power in terms of both damage output and debuffing when it comes to single targets.

That depends on if you're on a team or solo. If you're on a team it's easy. Prioritize your powers based on their debuffing ability and use whichever is highest on the list and is currently available. This list would be, in order from strongest to weakest: screech, shriek, scream, shout, howl. The attack chain that this would manifest as will depend on the person and their recharge values, but for most people it would be something like

begin fight with screech
shriek, scream, shriek
use screech if it's up. If not, use shout. If shout isn't up, use howl. If howl isn't up, use aim (amplify).

If you're solo, the best single target attack chain would be shriek, scream, shriek, shout. This attack chain requires 175% recharge combined from shout's enhancement values and from buffs/set bonuses, which isn't nearly as difficult as it looks. 70% can come from hasten and 80-95% can easily come from enhancements.

The advice I'm offering is based off of my friend's rad/sonic, who can solo AVs. He uses the power epic pool.

It's not. You should never be using howl in a single target attack chain.

Not in my experience.

If not shout, you could alternatively use that gap as an opportunity to use a rad power or screech.

Damage set bonuses are not the way to go when trying to up your solo damage with the invention system. I suggest taking most of your area attacks and proccing them out then playing on -1 or +0 with the number of enemies set to -at least- x3. Use cosmic burst and procced out neutrino bolt to finish off enemies.

People already have.

Shouldn't debuff resistance still come into play somewhere? I thought there had been issues with players resisting their own powers in the past, so it must be possible.

If you have a high recharge build then shriek, scream, shriek, repeat is plenty good.

Let's not kid ourselves into thinking that VEATs are balanced with the other archetypes.

You're right, it's 3.5%. I got mixed up and was thinking of the numbers for steamy mist/shadowfall.

I'm sticking to my guns on electric fence being a bad idea though. You can use movement to keep out of melee very easily.

Build for area damage and take advantage of procs. Radiation blast can do tons of damage.

This is false. They self stack. You can prove this even at low levels without a lot of recharge by using scream twice in a row without any other powers. The damage will go something like 8, 10, 10, 10 and then 10, 12, 12, 12.

And yes, shriek, scream, shriek, shout is the best single target damage you can get while solo. If you're on a team against a single target screech will be better than shout.