I don't think any in depth analysis is really needed for the US. Lack of density is certainly a problem, but not the main one. In nearly every major market, broadband is dominated wholly by a single company through municipally granted monopolies. Cities do this because they get kickbacks from the ISPs and other concessions like internet for unprofitable (poor) neighborhoods. In our system, ISPs offer an palatable municipal tax (by any other name) whereby the ISP becomes the hated party. Fortunately for them, ISPs aren't elected.

If you want faster internet in the US, start with your local government.