With the departure of instructor Alex, mostly there were only clueless and talentless alchemy apprentices.
Vincent stood at the back of the class and looked at how they purified their ingredients.
A couple of seconds was enough for him to assess that they were clumsy. It wasn't that they were terrible; they were just clueless and trying to mimic Alex, the alchemist. Their thought process was plain stupid. Their instructor flawlessly and efficiently purified the ingredients because he was a master at it. Even repeatedly doing what he did was going to lead them nowhere. It would take them some days to realize that and change their method of doing things.
Vincent realized all that because he was looking at the situation from above. As he had a better viewpoint, he could infer the wrongs and rights more clearly.