I do think you can learn a lot from group classes. I, myself was trained the first 3 years with group classes only. Mind you I was in my teens and didn't have the money to take privates. I had to pay for all my dancing by myself. I was lucky that the studio I was trained in, had both step classes and technique classes. There was 10 technique classes (all 10 international dances) and only two step classes (one for standard and one for latin) a week. I know several dancers that have ended up as national champions and even world finalists having been trained in group classes only. So if the group classes is constructed the right way, the teacher has the knowledge and the students are willing to learn, then you can go really far with group classes. I have however noticed that many studios in the US use the least experienced teachers for the group classes and that will of cause not produce high level dancing. You need to look at the teachers teaching the classes and the policy of the content of the classes for each studio to determine if you should go the group class way or the private lesson way.
Dancepro