The problem is that you think you need to sacrifice Defender or Berserk. You don't. You can get both skills without needing to sacrifice one or the other. Stryfe maxed bowling bash on the DPS. Bowling Bash is NOT in any way useful for damage because you can only use it once every 10 seconds. It only builds rage and that's the main use of it. Even if you maxed out Bowling Bash, 1 bash is STILL better than 1 bowling bash. Bowling Bash is as useful as Cross Impact.
Not once did I even mention or even suggest getting max Bowling Bash. In fact, I agree with you that BB should be kept at level 1, it is purely a skill to build rage and has terrible DPS in terms of damage output.
That said, maxing Bowling Bash or not is irrelevant since you still need to sacrifice one tree or the other to fully develop the other. I say this again: It is ludicrous to expect tank Warriors to have Rage Strike 5 (and Berserk 5 for that matter) or DPS Warriors to have a developed Defender tree beyond maxed Tension Relax.
Leveling parry is optional. If you're mobbed, you won't block all the attacks. If you're attacking a boss, sure it's okay. Even so, parry caps at 70%. With level 3 parry, it bumps you at 94%. You have a 94% chance to parry which is almost 100% of the time. Even having 80% parry already guarantees you parry every attack. Defender is a must no matter what build you do because you can turn it off if you don't want it on.
Someone proved that parry caps off at 100%, so that already is a reason to grab somewhere in the vicinity of level 3~5 Parry (I'm personally maxing it). Parry is one of the stats that Warriors clearly trumps Knights at from the beginning and Parry serves to further exemplifity that characteristic.
You don't need to spam Aura Strike on a Warrior. On a Knight, maybe yes. On a Warrior no. If you're raiding and tanking damage then you focus on keeping your rage at 100% incase you get nuked so you can heal yourself with Tension Relax and use Endure with it. You're not there to primarily deal damage as an OT because you let the other classes handle that. If you only have Tension Relax without Endure, you're dead. You can't have under 50% of your health, use Tension Relax and wait 20 secs for it to heal you all the way.
Warriors need to spam Aura Strike in their DPS rotation just as much as Knights do, Aura Strike is essential to make sure you are properly generating enough threat that your DPSers will not overtake you and so that the boss dies that much quicker. Even in a situation where you absolutely need to keep rage near max to be able to fire off Tension Relax at a moment's notice, it does not take long to go from 70->100 rage after firing off just one Aura Strike.
I am in fact finding it strange that you advocate grabbing Rage Strike (I also assume you're maxing it?) as a tank Warrior, Rage Strike would be a far bigger rage drainer than Aura Strike will ever be for a questionable difference in DPS and AoE which may or may not be useful.
You do realize I still have Aura Strike right?... I use it when I'm waiting for my TR to cool down, I don't use it for anything else so I don't find it useful to invest points into. Aura Strike builds DPS. That's the whole point of using it. I have it at level 1 and it's 37% damage. Level 5 is 45%. It's only 8% of a damage difference maxed. It's not much of a difference for me to care about putting points into because I don't spam it. It would be nice maxed, but either I max Aura Strike or get Defender. I'm getting Defender. It means I sacrificed 8% damage for a +30% defensive buff. Combined with Berserk... it's more than enough to negate the 8% damage difference. That's what sets Warriors apart from Knights.
If you were to have maxed Aura Strike instead of Berserk, that is a constant damage boost rather than a temporary one and also does not carry the -10% dodge penalty which basically equates to taking more damage as a tank; you do not want to do anything that will make you take more damage than what you're already taking as a tank. I would even argue that as far as the whole "sacrifice defense to temporarily boost attack" gimmick goes, a Knight's Concentration trumps a Warrior's Berserk simply because it lasts longer and is thus more consistent.
TR/Endure combo is because healers aren't going to prioritize OT's. When your HP falls below 50% there's a good chance the healer can't keep up with the heals or your entire party just lost 50% of their HP. That's why you use Tension Relax with Endure. Endure keeps the boss from killing you and Tension relax stalls for time so the healer can get around to healing you. Like I said, you can't wait around with under 50% of your health expecting to be healed. You throw on Endure for those purposes to make sure you don't die. It's insurance. It's even better if Warriors can time their Endures before a nuke.
Both of the hypothetical situations that you and sephiroso described are situations that can happen in reality and both are legitimate examples of ways to use a Warrior's defensive skills. Yours is an example of instantaenous burst sustain (basically hitting the "oshi--" button), while sephiroso's example is that of sustain over time attempting to keep yourself at a higher level of sturdiness for as long as possible by staggering your defensive skills. Both situations are legitimate and correct, but what this most importantly shows is that Tension Relax is indeed very useful even by itself contrary to what you suggested. If we are to also take into account generic soloing, the usefulness of Tension Relax simply explodes an order of magnitude larger.