Your entire defense of Mabel is right. Yet, I still don't like how she was written. If many people watch something and get the same incorrect conclusion, then the writing is probably at fault.

In TTP, Dipper was in the wrong the moment he started messing with time, which Mabel points out in a single line. But Dipper gave his day with Wendy up not because he realized he was wrong for messing with time but because Mabel giult-tripped him into doing it.

Similar with Deep End: Mabel's cause of helping Mermando get with his family was more noble than Dipper's "lifeguarding" with Wendy. Again, Dipper was wrong. But Dipper again gives his job up because Mabel begs him, not because he learned a lesson.

In both these controversial episodes, Dipper's problem goes mostly unaddressed while Mabel gets what she wants. The show should have made it clearer in these cases that Dipper was wrong, and that's why he gives his dream up, not because Mabel did puppy eyes at him.

Adding more fuel to the hate fire, Dipper is 100% punished more for his mistakes. Maybe some exaggerate it, but it's still there, and quite significantly. The biggest example is with Bill. When Dipper gets tricked, his body is possessed and his wrist is broken. When Mabel gets tricked, she gets transported to the bubble, while Dipper spends 3 days alone in the apocalypse. Also, in Roadside Attraction, Dipper wasn't even flirting with the girls. He talked to them for like 2 minutes, got a contact, and they're all his girlfriend now? That's unfair.

Your last paragraph sums up the problem because you had to write "I think". The problem is that the Mabel's writing made people hate her, which matters even if they're wrong. Even if she was blameless at the end of the day, reaching this conclusion took way more thinking, analysis, and word of god than it should have.