They aren't capping things because the rewards are valuable and need to be protected. They are capping things because people need to be protected from themselves. Trying to grind rank will do nothing but burn you out on the game and seeing so many high-rank players so quickly will discourage the people who are playing at the intended pace.

I don't understand how they're going to nerf Gruntpocalypse. Most of the earn in that mode comes from Commendations. All they can really do is turn the base "match complete" cR down to 60.