Everyone has their own mindset on how the belts transition. I find it similar to other arts (TKD vs Karate)...both very similar, but different in their own right. For example, I'm a purple belt in BJJ, but a blue belt in 10P. I don't feel as though I deserve a purple in 10P unless ranked by someone in 10P (my blue belt came from Derek Stewart) and want to make sure that I rep 10P/BJJ to the fullest; while not hiding the rank differences. Derek and I both agree that it is different, but share a lot of similar traits and techniques. I like that you can keep your rank for the most part when you transition, but I think the rank should not transfer so easily (BJJ black belts are brown belts in 10P until promoted). There's a definite lag in technique from BJJ to 10P just like there would be from 10P to BJJ. Unless you train both, then there should be a rank difference until justified. Respecting those differences, while keeping in mind the similarities (origin).
From my experience though, most 10P blue belts I've come across destroy BJJ blue belts any day of the week, then it evens out for the rest of the ranks depending on the skill levels of course. I say keep your rank in the end, because it does show that you've trained, but accept the fact that the two have a degree of difference that can be an advantage as much as a disadvantage depending on game being played.