This is highly variable depending on practice-type, setting, geography, etc (these are the kinds of questions you can ask in a job interview). I know dermatologists who see 20 patients a day. I also know dermatologists who see between 80-100 patients per day.
Generally, if you work in an independent private practice setting as a general dermatologist (I assume that's what you're describing?), you'll have to see more volume of patients to make the same $$$$ because the reimbursement is lower if you're not affiliated with a larger organization (less bargaining power with insurance companies). You can hire more MAs, scribes, etc. to increase efficiency, but these also cost $$$$$. The benefit is you get more flexibility and independence in decision making about how your job looks.