Gumball and Penny's issues can be boiled down to Penny being written as Gumball's love interest rather than her own person and Gumball being seemingly more in love with the idea of Penny than anything else. He often ignores her and disrespects her boundaries but she stays with him anyway despite these red flags because that's what she's supposed to do as a love interest. Honestly this ship and other similar ships that pair a loser guy and a girl who's way out of his league just comes across as self insert wish fulfillment for any loser guy watching. Now wish fulfillment in fiction isn't always a bad thing but it definitely is when it tricks guys into believing that they're owed female attention when they've done nothing to deserve it and as a woman, it just frustrates me.