Although I think it's a good and important discussion, let's keep on topic and not discuss the defense tier gap (which can instead be found
here).
In regards to expertise, I think we need to ask ourselves the following questions:
1) Should feats be relatively equivalent in power/effect?
2) Is expertise equivalent in power to other similar feats?
3) Is there a deficit in the math supporting the game mechanics related to PC attack progression versus monster defense progression?
For the first and second points, I don't think that it is helpful to bring in the argument that a power of a feat is defined by when a PC will/must take that feat. As other people have posted, players are varied in their play style and in how they get enjoyment from the game,
Instead, when looking at the feat, you must compare it to other feats, specifically feats that have a similar mechanic. Thus, it is not helpful to compare expertise to any of the feats that grant a bonus to skills, since they are affecting two different mechanics in the game. The better comparisons are between either feats that grant a bonus to damage, or better yet, feats like Nimble Blade.
Because of its lack of requirements (both to obtain the feat and the bonus granted by the feat), as well as it's scaling with each tier, expertise is a more powerful feat than nimble blade, and thus it is one of the stronger feats to take (at any tier).
However, I think that the first question cannot be argued or proved. It is ultimately up to the developers of the game to decide, although we as consumers and players should hold them accountable to it. While we all have our own opinion about this subject, the developers must decide whether they want their game to be balanced, and if it should contain power creep.
Finally, people have already gone through and done the legwork and math to show that the last point is true and relevant. Whether this was an oversight or if it was intended for a purpose, people's opinions of this deficit are varied. I think that it would be very helpful if we received feedback to these questions from the developer, but barring that, many informed people seem confident in choosing a side and making a house rule to fix these questions and problems cause by this feat.