As far as your point, well, I don't see it. You could keep bringing it back to say you should only choose Fighter or Mage. Or, hell, just "Adventurer," and have the bowslinger mage 'adventurer,' or the psionmagic swordmager 'adventurer.' They all fit under the same 'broad archetype' of adventurer.
Reductio Ad Absurdium doesn't quite apply here. I'm not arguing that we pursue the very simplest possible class structure. I'm just saying that it seems to me that the Seeker and the Battlemind (and some other classes, to a lesser degree) don't appear to have a clear archetypal reason for existing.
On the other hand, I totally see the difference between, say, the Rogue and the Fighter. Or the Fighter and the Barbarian. Or the Fighter and the Paladin.
It's a grey area that's going to involve judgement calls that individuals may disagree with on exactly where the line falls. Some might say the Warlock should just be a Wizard build. I probably wouldn't, but I could certainly see a rational person making that case.
But, to me, it's worth examining why D&D has a class structure to begin with. It doesn't have to have one -- plenty of other games do just fine without one. But there's something about saying "I am a Druid" that gives the other people at the table a distinct mental impression that saying "I am a Seeker" does not. "I am a Wizard" gives people a different mental picture than "I am a Warlock", so that's a distinction worth keeping. Of course, that's going to vary from person to person, so I'd say we use the "lowest common denominator": if someone who wasn't a D&D player heard the words, would they (a) get an image of what the character was like, and (b) make a distinction between that character and a few semi-similar characters. If a complete D&D newbie wanted to choose a class, would the little description you gave them be different?
A class structure lets you hang your decisions on an archetype. A class is not just a bucket of related abilities, it is a
certain kind of character, with certain typical qualities.
So if we're going to have D&D different classes, they should each represent a legitimately different kind of character.
For me, the Battlemind and the Seeker definately fail that test. Battleminds don't seem any different then fighters who run instead of lock-down. Seekers don't seem any different then rangers who shoot fire arrows instead of trick arrows.
It's not just about having a mechanical difference, either. A Knight and a Slayer and a Battlerager are all quite a bit different mechanically. Is the Seeker any more different from the Ranger than the Slayer is from the Brawler?
It's more about the image that word conjures up in your head as you play. Which is a subjective call.
Now, it's possible to make new archetypes. D&D does this a whole lot. I think (debatably) 4e has done it with the Warlord. But it takes more than another 50 combat powers to do it. It takes more than mechanical tricks and a power source/role niche. It takes a certain broad idea of what such a character embodies, in and out of combat.
Nothing is going to change the Seeker as it exists. People who like it for whatever reason can still like it and play it. But if the rules for the class were repackaged as Ranger abilities instead, I think I at least, and probably a lot of D&D newbies, would be more inclined to check it out. Because saying "I am a Seeker" is meaningless to anyone who isn't big into D&D. Saying "I am a Ranger" is much clearer, even if you're the kind of ranger who shoots flaming arrows instead of the kind of ranger who shoots trick arrows.