I comment here because pretty much literally the same situation happened to me. The first teacher I worked with assigned me a Chopin waltz and Bach invention etc. Nine months later, my second teacher, when I mentioned that I was interested in Chopin etudes, assigned me op 25 no 12 and op 10 no 8. And the teachers weren't unqualified, they had a Masters and doctorate respectively from decent schools and the second was established in the city. Given all of this happened with me, I'm not surprised that a teacher would assign a Bach invention, especially one fairly new to teaching.
Now, I also learned the first page of op 10 no 8 and the entirety of op 25 no 12 within a month which complicated matters, because according to traditional teaching methods, teachers will assign a piece and if a student can play it they continue with that piece. It takes a very experienced teacher to notice all the fine things which are missing. Perhaps that teacher noticed what was missing, but let me work on the pieces anyway because I was a "hobbyist". Though this teacher was experienced, newer teachers often run up against students who progress quickly and don't realize why they should take it "slow". The problem is that what's needed isn't exactly taking it slow, but instead observing and ironing out issues until they are learned well. However, many teachers are either incapable of this, or are afraid of students losing interest.
Also, as an adult, there is a common understanding that they can not learn proper technique because the bones/muscles just aren't formed correctly. I don't think this is correct, it's mostly a neural conditioning issue and the amount of actual strength it takes is something adults can definitely develop. But most people have not come to these sorts of conclusions, and this is exacerbated by the fact that a vanishingly small number of adult students ever improve at the piano beyond a point. The teachers had never seen a student like me, and it's fair to assume the OP's teacher may not have seen a student like him. The teachers also teach according to a vague recollection of how they were taught, which is usually similarly being asked to play pieces, and spending several hours practicing the details until they are learned. However, what they often find hard to judge is when a piece is too difficult, because as part of their development, they learned a very large number of easy pieces in a certain order and gradually just "got it". Kids often implicitly learn technique, and when a teacher sees that a student is able to play something, they often don't reinforce good habits out of some misplaced sense that the music is more important and that the technique is mundane. I know concert pianists who learned in this manner, largely intuitively, and maybe even later suffered issues, so people with some degree of natural talent often can get very far without truly good instruction.
Also, again, most teachers, and I'm speaking from experience, truly do not believe that an adult can ever learn the kind of technique a child would have, much as they don't believe an adult can change their accent. So they teach and give suggestions for incremental improvement, but rarely start from scratch and try to develop technique rigorously. This is what I mean by rigorous, it's putting in an enormous amount of time and effort until the basic movements are "perfect" and totally ingrained at a subconscious level. Now this can take place over years, but it makes sense -- even in my experience, I have never seen an adult willing and capable of doing this (except for other piano students on forums etc.). They often get dejected too fast, and want to do something fun instead. Also, the vanishingly few who are really serious probably seek out excellent teachers, so the average teacher is likely to meet exactly zero of them during the normal course of events, further reinforcing the idea that it's impossible. And then they don't want to disappoint adult students, but if you probe them enough (and I have), they will usually come clean and say that you will never have their technique because you didn't start as a child.
So they teach you according to what they believe can be taught, which in itself isn't a bad idea tbh. Like, we don't make kids grind IQ tests for a reason. And I am also not sure that most adults can relearn hand movements to the extent that they can play piano at an accomplished level. I feel like I can observe motor movements and sound quite well, and I have seen that not all people can to the same extent. I have met a few who have started piano late (13+) and play very well and they all have this trait where they have very good observational ability and are excellent mimics.
So this is what ends up happening much of the time. Adult student can play the notes in rhythm with some musicality? Okay, let's triage the piece and make the student work on different aspects of it and throw in some musicality. The end result is passable and most people can't hear the nuances of classical piano anyway, so how does it matter?
Topic: feeling overwhelmed