Critique partners should be of the same genre because each genre has conventions that might not appeal to writers of another genre. Take horror and romance for example. People who write romance and who are used to having happy endings would not like it when the monster everyone thought was vanquished makes another appearance at the end, while the horror writer might find it unconvincing that a dude would whip up a four course meal complete with fancy pastry for the woman he's courting and then not want sex.
Or women's lit and historical. Modern reader look at arranged marriages in novels and respond with "Why would a sixteen year old girl agree to marry a thirty year old man she's never met and doesn't love?" Answer, because if she didn't, her sister would, and sometimes the family could only afford to marry off one daughter, and the girls who didn't marry probably went to a convent, which in those days, was exactly like being sent to prison.
Not saying historical fans don't ask questions like that, but if you're going to change things to suit a reader, it should be a reader who might pay money for your book if they didn't know you.
