I recently played MW2 again and used the Spas-12. The 870 doesn't even come close. They should buff it, along with the other shotguns. Hell, even dual Rangers are better than it.
I don't get why you'd compare one of the most powerful shotguns in MW2 to any shotgun in any other CoD. If you would've said that the MW2 1887 (Post Patch) was better than the R870, then you'd have a more legitimate point. Saying the Rangers (let alone akimbo) is better is not really saying anything new at all.