Comment: many of these feats should probably be designated as fighter bonus feats.
We do in fact have different impressions of the Tier system. Since that's not really germane to the discussion, I'll happily agree to disagree with you and use different labels for things. Talking about the feats is more productive anyhow.
Regarding the challenge: You said that stock monsters from the Monster Manual would do fine as opponents. I invited you to test that theory. I'm betting your fighter chows through those opponents faster than a fat man at an all-u-can-eat buffet.
You haven't failed at anything; your feats are quite good. But I believe my numbers are defensible.
Looking at the first example, damage on AoO is 4d6+20. Breaking that down, we're looking at 2d6 (greatsword) + 1 (enhancement) + 3 (150% of Str bonus) + 6 (Blindside). The sum is then doubled by Entrenchment to 4d6 + 2 + 6 +12.
Looking at the second example, damage on AoO is a little more complex. We have 1d6 (short sword) + 2 (Str) + 6 (Blindside) + a possible 2 more if the target has already been struck by AoO this round (Expert Tactician). We have Double Hit, which entitles us to two attacks per AoO. Most likely we're looking at getting the Expert Tactician bonus only on the second swing of each AoO. Thus, each AoO is likely to produce 2d6+18.
Edit: Moreover, I wouldn't call this a corner case. Assuming the fighter is in front in most groups and gets more than his fair share of attackers (which is generally the fighter's goal), we're assuming 3-4 opponents, or 1-2 opponents that are able to move and full attack. Perhaps my gaming group is unusual, but at my table it's common to see enemy groupings of that type (or even larger/more capable!).
I won't deny that your build is representative of a typical fighter, but it differs from mine in two important ways. First, you used 32 point buy, while I used elite array. If I switch my builds to 32pb, their damage and accuracy improve considerably. Second, you credit your build with damage from AoOs, but you have no way of forcing the enemy to grant you those AoOs. The extra 75 points of damage are vapor damage, impressive on paper but not likely to happen in a game. My builds use your Counterattack feat to force AoOs when the enemy attacks. Without the ability to force AoOs through Counterattack, your build's expected damage drops about 85%, from 90 to 15.
So, assuming that you agree with what these builds seem to be telling us, which is that Blindside, Counterattack, and Entrenchment are a darn good way to deal over a hundred damage per round by 6th level, here's the next question: do we want to be dealing 100+ damage per round at that level? Assume a typical EL6 encounter is a group of 4 CR2 monsters. CR2 monsters have about 15 - 35 hp, depending on the critter, probably averaging 25. We're dealing enough damage to kill the entire encounter in round 1 even if one or two of our attacks miss, not even considering the contribution of the other three adventurers in the stereotypical party of four. Is that a good thing? What are your thoughts on this?
Edit: I really like Blindside. The more I sit and think on it, the more I'm thinking of ways it can combo. A lot of mobile striker builds find it very easy to end turn not threatened by any creature, meaning Blindside could trigger round after round. Lots of possibilities in that one.