Except that every sentence here is wrong.
Yes, Brodie is having the best statistical season of his career with Rielly at 56.8xgf%, far surpassing anything he did with Giordano. Brodie has had the luxury of playing with elite puckmovers like gio and rielly in his career - and his years where he was forced to be the puckmover when paired with guys like Hamonic it was disastrous.
And yes, Rielly is also having the best statistical year of his career, now that for the first time in his career he has a legitimate top pair dman to play with, instead of barely top 4 guys like hainsey and the corpse of phaneuf, or #6 guys like ceci and zaitsev. This is no surprise - brodie is a much better dman than those other scrubs rielly had been forced to carry.
Rielly is an elite of elite puckmover, both in skating the puck and passing the puck, both out of danger and into the attack. That also happens to be the most valuable and the most difficult skill a dman can have.
As for your tiny muzzin-brodie sample....muzzin-rielly has even better xgf and xga than that pairing does, in a sliggtly bigger sample. Not that any of those samples matter of course.