Here's where we differ. I don't see them as unbalanced, but rather an option. Would that they have been worded more compex (such as only weapon-using characters with a 16 or lower attack stat and a +2 or non-proficient weapon) I think they would have been better, but then they become needlessly complicated.
Just to again clarify, I said "unbalanced compared to other options". I don't believe they actually break the game, though I do believe they are harmful to it.
But I don't think you can deny that they aren't balanced against other options. Many other feats offer you, say, a conditional +1 bonus to hit. Often under specific circumstances like having combat advantage or making an opportunity attack.
Expertise, in return, offers a scaling +1/2/3 bonus to hit, effectively all the time. And, these days, often includes other very potent benefits as well.
If one operates under the idea that the idea of a 'feat tax' is incorrect - that this feat is not
required to be taken, and that it is intended
entirely as a normal feat to be measured alongside other feats, it clearly has not been balanced in the same fashion that other feats have. Which is, normally, terrible game design.
The argument that is made to answer this is that it is a 'feat tax'. I don't see anything insulting about the term - it represents the belief that the designers feel everyone should be taking this feat, and that it is intended to patch an issue with the core math of the game. As such, it isn't subject to the normal design limitations of other feats.
Thus, some believe it is overpowered but that is fine because it serves an important role in the game. Others feel it is simply overpowered and isn't needed at all, and thus is problematic. And others might find it overpowered but not enough so to actually care, which I sense is the area that you fall into.
But I don't think one can suggest it is appropriately balanced against other options. And in my mind, it doesn't help characters who start with 16 in a stat and a +2 proficiency weapon... instead, it only helps make it possible for them to be farther and farther behind.