I am in my first year of a Ph.D. program in the humanities at an R1 University. When I applied and went on the campus visit, it seemed that the department was more focused on my subfield than it actually is. While, on the surface, it seems that my interests meshed with particular faculty members but, after getting to know the faculty members and their work more thoroughly, it turns out we really have little in common research-wise.
You have been humbled (?) and feel insecure. You need to trust someone where you are to acclimate. When you become a small fish in a big pond, there is a lot of room to move around. Investigate faculty and course offerings in other departments. Socialize. Your research is ostensibly interdisciplinary, if I remember correctly.
Change your learning strategy and summarize what you took from each of your seminars. Then apply it to one of your pet projects.
You will notice I have said roughly the same thing SD did.
You're certainly right to point out that one needs to be self-reliant in addressing lacunae in his or her graduate education, but it's hard to deny that it is optimal to work in an environment (by way of profs, fellow grad students, and resources) conducive to one's particular scholarly interests. It also seems valuable to have an established prof. working in your specific sub-field (as opposed to any prof in the discipline who may know only peripherally about your research specialty) speak for the quality of your work when job hunting.
I was in the OP's situation a few years ago, and opted for a transfer to a dept. more focused on my own line of research. Decision to do so hasn't been regretted.