That's a good analysis of AC vs. hit points through feats Gaiden and I think it's a good analysis of the game in general for tank types.
However, I think you overestimate the significance of some of the other options. Take your analysis of the character lasting 3 rounds against the BBEG. The BBEG is dealing 18 points of damage a hit on average. That kind of damage output probably means the BBEG is using a greatsword, greataxe, or other damage dealing weapon which probably puts his AC around 26 or so (+3 fullplate, 12+dex, +2 deflection, +1 natural armor or some similar getup--if we toss potions of speed or alliesinto this we could reduce the rest of the treasure or boost his AC to 30 but this is a stand alone BBEG). The PC in question has a raging strength of 28 (decent bull's strength assumed) and let's also assume a +2 greatsword. That adds up to +21/+16 to hit and an average damage of 24 points per hit. Munchkin damage calculator
http://www.public.asu.edu/~tarchon/munchkin.html
estimates that the PC will inflict an average of 32 hp/round on BBEG. Assuming that the BBEG has three levels on the PC, a conservative estimate is that he has about 127 hp or so. By himself, the PC will take 5 rounds to finish off BBEG. That's about seventy hit points of healing the PC needs in order to survive
If I drop that strength to 24 (in the event that the PC has already used his rage for the day), that damage drops to 23/round. The PC now needs 6 rounds in order to finish off BBEG. Which is about 100 points of healing.
In this case, extra rage adds to the character's offensive power and has a similar effect to the combination of Dodge and Armor Focus in terms of damage the character takes.
On the other hand, a character whose regular AC is 34 (like the spellsword in my earlier analysis) can extend his lifespan from 5 rounds to 8 rounds against the same bad guy (although he obviously will be relying on other characters to carry more of the offensive load) by taking the same two feats (or two that also give him +3 AC such as Shield Specialization and Armor Focus). To me, it looks like the higher AC spellsword gets much more milage out of the AC boosting feats than the barbarian.
Obviously that's a very simplified analysis (it doesn't figure in allies on either side) but I think it points to feats for offensive being more effective for this character than feats for defense.
Also, I think it's worth considering how other defensive feats like Close Quarters Fighting will enable the character to decrease the number of rounds he fights by increasing his damage output. At a minimum, the character can expect to get an extra 24 points of damage out of Close Quarters Fighting (the average damage on an AoO). If it also enables hit to avoid being grappled on the next round (not guaranteed since many creatures (dire bears for instance) are capable of two improved grab attacks per round and CQF only helps against the first one--but still likely in many situations), it may well give him an extra 64 points of damage (24 points on round 1 AoO, 24 points on round 2 AoO, plus the difference between the 32 points he regularly deals with a greatsword and the 17 or so he's likely to deal after drawing a dagger to attack his grappler) points of damage. That difference probably amounts to knocking at least two rounds off of the combat--twice as good as the combination of two AC feats. . . although only applicable against certain foes.
It's a very good point about Blindfight--I assumed the character wasn't on a swift prestige class progression plan. If you are and don't want to take another Barbarian level, blindfight is excellent. (All the more so because it opens up new tactical capabilities as well as defensive ones).