Ron is not stupid - he canonically gets good grades despite spending most of his time goofing off. I spent a year literally falling asleep in Algebra I in high school and still passed with a B despite it being my most hated subject, I can easily believe he managed the same feat with Potions.
I'll take the hit on having fallen for a strawman, but what I was trying to say is that it takes fanfic to turn Snape into the kind of character JKR seems to have intended him to be from his death scene and Harry's reactions, rather than what she actually put on the page. How that usually turns out is indeed irrelevant, the point is that all the in-classroom evidence we actually see (and most of the rest) is of him failing to engage as an educator and indulging in his personal biases against Harry specifically or struggling students and muggleborn in general, to the point that the few times when he does something actually helpful for anyone but his junior Death Eater Slytherins it's wildly out of character.
I'll take the hit on having fallen for a strawman, but what I was trying to say is that it takes fanfic to turn Snape into the kind of character JKR seems to have intended him to be from his death scene and Harry's reactions, rather than what she actually put on the page. How that usually turns out is indeed irrelevant, the point is that all the in-classroom evidence we actually see (and most of the rest) is of him failing to engage as an educator and indulging in his personal biases against Harry specifically or struggling students and muggleborn in general, to the point that the few times when he does something actually helpful for anyone but his junior Death Eater Slytherins it's wildly out of character.
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‎noli esse culus
‎noli esse culus