There is always hax but every fighter adapts his body based on the DF he eats, its not like luffy was born a brawler but having something like gomu gomu made him grow up as a physical fighter due to not having other choice at all, maybe if law ate gomu gomu at a young age then he would probably be a brawler like luffy is right now or vice versa if luffy eats ope, gomu gomu is not weak, actually its pretty good stretching, expanding and getting techs like G2,3 or more makes the DF pretty formidable, it may sound weak but its pretty good, its more of who uses it rather then the DF power or hax, u just train ur DF beyond weakness and then there is someone like Mr.5 who makes his DF look shit even though its pretty good.
I'm not denying that there are stronger fruits then the others but it mostly matters on the user of the DF.