Mars atmosphere can barely be called that. It's less than one percent of earth's pressure. People just have a wrong perception of it because of wildly inaccurate depictions in movies like The Martian. And even if you want to transmit using radio between the surface and low orbit, it's far less of a bandwidth issue than transmitting over millions of kilometers. Deep space transmissions of the future will use optical wavelengths instead of radio, there's no question about it.