You know what’s some bullshit?
People who make call out posts about characters without closely reading the text first.
Snape knew the potions textbook sucked.
He knew exactly how it sucked, too; his own copy was full of specific revisions that totally worked for a non-prodigy kid. We don’t see him assigning that specific textbook, as by the time we see the textbook in class, Potions is taught by Slughorn and not Snape.
But we do see Slughorn teaching by the book:
“Scales out, everyone, and potion kits, and don’t forget your copies of Advanecd Potion-Making…”
Contrast this with Snape, who uses the blackboard:
“The ingredients and method” - Snape flicked his wand - “are on the blackboard” - (they appeared there) - “you will find everything you need” - he flicked his wand again - “in the store cupboard” - (the door of the said cupboard sprang open) - “you have an hour and a half….Start.”
Snape didn’t “let them all fail forever” - we know that Tonks passed Potions, as she became an auror. We know that Hermione gained an Outstanding OWL grade under Snape’s teaching, and that Harry gained a perfectly respectable grade - as did Ron - despite Harry having the most difficult working conditions in that class (teacher and student actively despised each other) of any student in canon. Snape’s expectations for his class is high - he expects them all to pass, and he’s permitted to have a higher acceptance standard for his NEWT level class. Even Umbridge remarks that his class are advanced for their age
It seems your attack should be focused on Slughorn, not Snape. He’s the character who teaches from the book. He’s the character who presides over Hermione - an outstanding student - starting to fail at NEWT level, all whilst not noticing that Harry is cheating with all manner of shortcuts.
So yes, it’s Slughorn who is exceedingly good at potions, but he, the Potions professor, actively prevents younger generations from getting good at potions?
What a dick.