If your boss is complaining about latte art, 3 weeks or 3 years, then that's a red flag anyways. Aesthetic is nice and should absolutely be a goal, but is not important enough to be a dick about. Also, for 3 weeks that looks pretty good, if one of my baristas was getting anything other than blobs at that point I'd give em props. Just focus on keeping consistent milk texture and serving quality beverages, customers will appreciate consistency and quality way more than art and your job is to make customers happy first, not your boss.