If if get you right you are saying:
The Batlerager is balanced because his defensive capablilities might be too good, so that he won´t be attacked anyway?
A battlerager that goes too far in making himself a tank (i.e plate armor and a heavy sheild) will also be giving up a lot of damage output as a result, since they don't have the attack bonus of the other class feature, they may have given up on strength, they are wielding a 1H weapon and they aren't getting the built in damage pump from the class feature.
Harder to hit + lower damage output = less of a "threat" to the monsters and thus not as intimidating of a defender. There is a point where the monster/DM is going to see attacking the striker/controller as tempting enough to take the penalty from being marked AND take the combat challenge attack.
This depends on the DM though ... if a DM is one that (almost) always respects the mark, and doesn't provoke OAs, than by all means make a fighter have the highest defensive possible, ignore his wisdom, etc, etc, etc.
Intelligent enemies might have the choice to ignore the Battlerager.
But why would enemies with below than average intelligence (i.e. most monsters, undeads and the like) "chose to ignore" the battlerager?
Either they are drawn to his shiney armor, and thus go after him ... or they go after the rogue or wizard with much more exposed flesh.
Considering the monsters have some understanding of what marks are, they have to make a decision based onhow to react to it. The unintelligent creature is just as likely to ignore the mark as it is to respect it.
What does a Zombie, a Hydra, a bunch of stupid koblods know about heroic classes an their features, that they chose to ignore a certain character?. What can they learn in the couple of rounds they are going to live to make such a choice with an int score of 3 or 4?
When you see a guy in plate with a shield, it's not a mental leap to think "he is hard to hit". If the fighter hits and the rogue hits for a lot more ... instincts are the go after the guy that hit you harder, although some will just attack whatever is in front of you.
Seriously, if you see D&D as a Tactical Miniature Battle, it might work out. Just bring a few artillery with you and focus on the battlerager and let your mellees ignore him, even though he will mark them. No big deal, the Battlerager is balanced.
But in a ROLEplaying game, I as a DM do not want to have Zombies and the like act this way, just because this is the only way I can put up an exciting encounter. My "low int" monsters will attack anybody who is in front of them, and if somebody marks my monsters, they rarely need more than this for a reason to attack him, unless they are very wise or smart ones (i.e. Dragons, Experienced humanoids).
So, if you DM a specific way, battleragers can be much more powerful. Of course by having the dumb monsters ALWAYS respect the mark ... you make it so that any powers related to "improving" the mark and related powers, wasted feat. Much like a DM that will rarely provoke OAs unless the players force him into it makes heavy blade opportunity and related feats wasted.
Also, monsters that change their mind as to who they want to attack, based on the threats of another creature ... seems like something that requires intelligence. It can easy to be justify monster behaviour either way in terms of the mark. Either the fighter "gets it's attention" and it's so easily distracted that it ignores the rogue, or it's so mindless that it ignores the mark and keeps going after the rogue that hit him (especially if they fighter's attack missed). A DM can still make a fight challenging and interesting without making the monsters super geniuses. Also, if the groups are constantly against "all brute/soldier" type fights, then of COURSE the battlerager is going to seem broken, if everything is melee and close. If the party went up against nothing but huge masses of minions and swarm monsters, the wizard would be the MVP.