All right, so I've had some time to kill the Archdemon and ruminate on the build. I think most of us already know archery is a bit underwhelming, so I'll try to avoid dwelling on that. Inc long post.
The power curve of this build was not what I expected. I made a beeline for Master Archer for that early +30 bonus to defense, but it really wasn't all that useful. A number of the early "hard" fights completely negate defense (wolves overwhelming, Ogre, Uldred), and since I was trying to get AoS and Master Archer early, I raised dexterity at the expense of strength. Consequently, I was late wearing heavy armor, and still couldn't tank effectively even with defensive fire. The bandits at Lothering and pretty much everything else could still chew me up in a hurry.
After I got AoS, I picked up the Champion spec and invested in that and the warrior tree, moving toward Deathblow. My logic was that I was still too squishy and that without deathblow I wouldn't have the stamina to use both Scattershot and AoS regardless. This was a mistake. In fact, going for AoS early was a mistake--I should have gone for Scattershot first, I think. Leliana did pick up scattershot, and Sten had 2h sweep and Alistair had DW sweep/whirlwind, so my PC was the only one with no aoe damage capabilities. Additionally, it was too easy for Leliana to get killed by pulling aggro on archers with Scattershot, which I had no good way of pulling off her.
AoS was fairly useful as a quick way to eliminate a single enemy, but as a non-templar and non-rogue I wasn't impressed with its capabilities as a mage-killer. I always had to have someone else in front of me to kill a mage with it, or I would get hit with crushing prison. It was useful to take out half an elite mage's health, but I found Alistair to be all-around better at the job, from being a templar of course.
Scattershot is really the only leg up the archer has on the S&S warrior. It lets the archer get the attention of all the enemy archers without having to worry as much about positioning. One mild surprise I found was that I ended up using Threaten, something I haven't done since my first game. It was actually quite useful, especially with Frightening Appearance. I suspect if S&S warriors had any sort of area effect attack, they would use Threaten more as well. Threaten + Frightening Appearance + Scattershot = long range taunt.
I said before that early on I was not an effective tank. When did I become effective? About the same time any other tank does, around level 10. By level 15, in line with previous experiences with a "normal" tank, I was quite tough. The gear I ended up using, as I said earlier, was mostly the same gear I would recommend for any tank: Evon the Great's Mail + Diligence Gloves/Boots, Lifegiver, Andruil's Blessing, Blood-gorged Amulet, and Helm of Honnleath.
Once I was fully realized, in terms of toughness, I would definitely put it on par with a classic tank build. You actually end up surprisingly weak vs archers, because even with the best gear you're behind a S&S tank's natural bonuses vs ranged weapons. Fortunately ~40 armor cancels most of that out even when they do hit you, and decent health regen takes care of the rest. I believe I tended to take more damage than Alistair did in the last Cauthrien fight, but that could have been because Morrigan wasn't around to CC everything and prevent the stuns. I definitely died pretty quickly to her without defensive fire up.
One question I think several of us had was, "How effective can it be without knockdown immunity?" Fairly effective in most situations, but almost completely ineffective in others. I could not tank a dragon or an ogre, since I lacked both Shale's Grab immunity and the S&S warrior's knockdown immunity. Sten filled in for those, using Cailan's Armor's amazing health regen. I also built him raising str and dex in a 2:1 ratio, since I knew my whole group would have to be tough or die.
Another idea that was brought up before: being a higher damage tank, or a character that could switch from damage to tanking mode in a pinch. First, I wouldn't recommend tanking without heavy armor, but I suppose a damage-oriented archer wearing Wade's heavy stuff could probably fill in for some fights in a pinch.
Second, you are not a higher damage tank when defensive fire is up. At least, it didn't feel like it. 50-60 damage every three seconds isn't a heck of a lot, and you're not going to be using a lot of abilities when you're actively tanking something tough enough to warrant defensive/suppressing fire (you can have both active). Between rally, suppressing fire, defensive fire, taunt, and using warcry every time it's up, you really don't have anything left for a lot of actives.
The specializations I used and would recommend would be the same as those for any other tank, and for the same reasons. Nothing more to comment on that. And to compare this to a rogue archer... I really can't. The rogue archer isn't tanking and doesn't want to. Those are all my thoughts for now.
Watch
this playlist or scroll back up the thread if you want to see the three videos I posted from this run.