While this might be true for maybe population size or territory, the govermental structure is completely different. ..also there are huge cultural differences (language; diff. social path dependencies etc.)

I don't think the similarities justify comparing US states to European countries.

No, you shouldn't. European nation states bear little resemblance to federal states, neither historically, culturally or economically.

The point was not that comparisons between states and cities are somehow more valid, but to illustrate that the differences in higher education are most likely due to the vast population difference.