Most beat'em ups are hyper competitive online and very often 1v1, meaning there is only really win or lose - people that are new to the genre will likely have no chance to get any gratification in that environment and the far majority of them will simply stop going online (resulting in online being even more dominated by skilled players). Unless there is some really compelling single player/coop content these games are imho not likely to really grip people that are new to this.
I've personally played quite a varity of beat'em ups over the decades, some of them for hundred of hours, yet I never go online either, as I just get annihilated.