I feel like Mrs. Rabbit is probably the bigger "oh, she's just cheesecake" of the pair here, and I will get to that. First, though, I feel like many people fail to realize how much Jessica embodies what Betty stood for. Far beyond both of them being "sexy" singing characters, there is so much feminism in both of their characters. They might both seem like soft women, but both of them have cores of steel.
Let's be honest, despite the "damage" done by Paramount adopting The Hayes Code in 1934, Betty Boop was an icon of sexuality in her time (and still is, really). She was one of the first cartoon women to appear on-screen whose existence was intended for a mature viewership. More than that though, she was a representation of the flickering hopes of the Jazz Age as the Depression wore on. And sure, there are elements of that aspect of her character which are a bit contentious. Since she was originally a caricature of Helen Kane, a lot of her style is based on the white co-opting of the culture of Harlem. Either way, she was so wildly popular that the anthology series she had debuted in was eventually turned into The Betty Boop Show.
In one of the first episodes of that show, Minnie the Moocher, Boop was portrayed as an older teen railing against her strict, Yiddish parents. That spirit of rebellion had long since infused her heavily caricatured, Flapper-inspired design. Coming from an era where women represented in animated features were either intensely childlike or merely feminized versions of their masculine counterparts, Boop being a sexually mature woman, who wore "sexy" feminine clothes, was a titanic shift.
That sense of female power was not just in her "challenging to power" appearance. Boop's cartoons also dealt with the male-gaze baggage that came with her identity, especially in the featurettes Chess-Nuts and Boop-Oop-a-Doop, where she directly encountered attempted rapes after rejecting men. Her claim to bodily autonomy in a media production was years ahead of its time and a huge step in both representation and the ever present fight that "cartoons" are just for kids. When the Hayes Code took effect, however, a lot of that faded away and Betty became a more demure housewife.
Fast forwarding to the 80's Boop's cameo in Who Framed Rodger Rabbit, where she was once again voiced by long-time VA Mae Questel, was a passing of the torch in a way to the next generation of cartoons. Jessica Rabbit, devoted wife and career woman at the same time, was a send off of the 50's-nostalgia-fueled sitcom wisdom that once a woman had gotten married, she had to stop being sexy and start being a housewife. Hell, we still have yet to get past that preconception.
Jessica being the perfect hourglass filled with distilled femme eros while being happily married to a guy who was gaga over her for not for her appearance but her passion and drive was also a challenge to men who treated women as objects to view and own. Mrs. Rabbit knows full well she is sexy, but she also has zero time for some guy's bullshit with regards to that. Going a bit more canonical, I feel like, if Boop had not had to deal with her own harassment, then Jessica's character would have ended up very differently. However, we got a woman who "grew up" looking up to Boop as a toon who was both sexy and her own woman.
For another take on the idea of performative appearance, watch Iliza's new special Elder Millenial where she has a tremendously funny take on how women are socialized to be noticed and how that's honestly (a little) fucked up.