There are probably more physical skills required at third base, but it's two different skill sets. 2B requires pivots and throws at second base which is a skill not everyone has. The big thing about 2B versus 3B though is they are involved in about 60% plays (interestingly it was 80% about 20 years ago), so there are more opportunities to make mistakes. Thus, it's more crucial that the 2B is steady and sure handed and consistently makes accurate throws. This might be more mental than physical, but they are still skills.
What I find interesting about third base (as you also suggested) is how the profile has changed so much over the years. Back in the early 20th century, it was considered a defense first position and there weren't a lot of good hitters there. Then over time, it became more of an offensive position and eventually got to the point where it was considered a power hitting position almost like first base. In recent years, defense at third has become important again. They are expected to be able to hit for some power too, but that is true of middle infelders now too.