It's true that weapons don't exist in a vacuum, and it's possible that a greatsword really is more useful because of that +hit, but in a world where the bastard sword exists and feats are cheap, it's pretty hard to claim the greatsword is worth anything.
This is what I don't understand. Yes, a bastard sword is a better weapon in 4e than the GS. That's....the point. Its a superior weapon, you pay a feat and get to use a better weapon.
Now if your point is that currently there aren't enough good feats in 4e to provide competition to the bastard sword feat than I agree with you. But that has nothing to do with the GS. The GS seems to be a solid weapon, it trails just slightly behind the other THW in damage, but you gain the reliability on minions and better landing of non damage effects. The BS provides a solid boost to that weapon for the cost of a feat, exactly the benefit you should get for a feat.
Wait until some splats come up with a lot more feats, and suddenly you might like the GS because that means you get to spend that feat on something else, something you really like. But that's a feat issue, it has nothing to do with the equipment as written.