So, I’m not the brisket pro. Others here have a ton more experience with brisket but if you had a chewy brisket, I don’t believe it was done rendering down. You said you cooked to 190* but it could have needed 10* more depending on the piece of meat. The first brisket you mentioned was dry, it could have been over cooked. Each is different, so the advice given most is to pull when you can probe the brisket and it’s like butter. If you had a chewy brisket, I’m guessing it would not have probed this way, but I could be wrong.
Also, what size of brisket and grade are you smoking? That can also play in how it will turn out.
Don’t give up. I know it’s frustrating. I’m the same way when I don’t get the results I’m expecting. But journal your process each time so you can see how things go and when you nail it, you have it written down exactly how you went about it.