Honestly, even before i started shipping it, i liked how well they worked with and brought out the best in each other. They were a good power duo, and I think the only reason they didnt keep up that angle for the future series, was because they were afraid of (light, lets be honest it’s just cousins) incest implications. If they weren't related, I would still have liked it, and we would have probably gotten more of it.
Although if they weren't related, they might possibly have shoved in a bunch of overt ship-teasing of an obnoxious variety or, god forbid, relationship melodrama, which would change their relationship and dymanic for the worse. It really is an interesting what if.