I think a lot of people forget how intelligent Ginny Weasley is because she doesn’t spend all of her time in the library, unlike Hermione. Jocks can be genius too people! If you think about it each one of the Weasley children are fairly intelligent and successful.
I'm with you on Team Weasleys-Are-Smarty-McSmarties. They have two Head Boys, a handful of prefects, great OWL scores, two inventor geniuses etc. Molly and Arthur are doing something right with those kids, given that they are all brave enough to pursue their individual passions in their vastly different professional fields.
With Ginny, we know she's quick witted, coordinated and a great mimic, she has observational skills and imitation talents. I like to characterize her as a kinesthetic learner - I see her as an active person and picture her doing great in classes where she's actually DOING something - spells, potions. I think sitting still for long periods in a library would be torture for her, so it's easy to miss how clever she really is - she has a different sort of intelligence than Hermione.