The actual need of weekly lesson depends on two factors: 1. Your own level of competence, and 2. The level of competence of your instructor.
The first year I was in college I took two instrumental music classes as both met twice a week plus my performing in the college marching band. The class professor was also the band director. I'll compliment him by saying he was about as good as my High school instrumental music instructor / band director. In the one course I took my second year I had an adjunct instructor who was pursuing his Master's degree, and while I continued in band, his and my personality clashed and I do not feel as if he contributed anything toward my advancement and although I was graded low, I passed. Such was also a consensus of opinion by the majority of others in his class. He gave only 1 A, 2 Bs, 26 Cs, 2 Ds, and 8 Fs. It was noted that he didn't teach the following year, and he hadn't yet received his Master's degree.
Yes, some teachers are very good and some are LOUSY IMO. It is distance now that inhibits me. It's 34 miles one way to a university with a reputable music department. There is a really fine trumpeter on staff who will instruct me occasionally by appointment and he understands and has shown concern for my health and dental problems.
Yup, there are two sides to the coin.