It seems unreasonable to me to expect to be B1 in 6 months with 2 hours of class per week.
I've been learning German 2 hours a week + homework for 2 years and I'm not yet B1 in German. We are 4 students with one teacher and, from what I understand, we are not particularly slow.
Maybe German is really harder to learn than other languages, but probably not 2x or 4x as French (I'm French).
I'm probably C2 comprehension, C1 speaking in German. I self-taught to high B2 (based off placement into that level in a Goethe Institut Intesivkurs) in 15 months of 2 hours a day. I studied 1-2 hours per day on average and did not miss a single day.
2 hours a week to B1 in German as an English speak seems totally impossible. I was probably B1 in 6 months at the level of study I described. I studied 5 years of Latin prior to starting so the case system wasn't an additional learning curve. Your pace honestly seems standard.
People talk of "difficult" languages in absolute terms, but there is always the question of where one is coming from.
English shares a significant amounts of structure and words with French, so French ends up being relatively straightforward to learn for a motivated English speaker - the only real difference is the amount of tenses, which OP unsurprisingly still struggles with. I bet you, as a French speaker, would grasp Italian very quickly - much faster than most Chinese likely ever will.
German ended up sharing much less with Romance languages, so it stands to reason that it would take 2x-3x the effort of going from English to French.
I think language classes are in itself slow. Duolingo is a lot faster. After Duolingo you should read texts in the language (B1-B2 maybe) and then you will start being able to listen to arbitrary native speakers (which I don't think is practicable before C1).
French has plenty of difficulty in orthography and some in grammar. Maybe the grammar is slightly less complex than German, but only slightly. But I'd say for someone from another language that is easily overshadowed by prior experience in English or Spanish or similar.
I've been learning German 2 hours a week + homework for 2 years and I'm not yet B1 in German. We are 4 students with one teacher and, from what I understand, we are not particularly slow.
Maybe German is really harder to learn than other languages, but probably not 2x or 4x as French (I'm French).