I render in Cinema 4D, but I compose my animations mostly in Poser, using Daz figures. In this example (below), most of the animation is mocap created in Optitrack Arena, exported as bvh into Poser. In Poser I clean up the animation, add facial expressions and hand movements, then save the animation to be applied to Daz figures in Cinema 4D via InterPoserPro.

https://vimeo.com/60618286

The walking section (starting 55 seconds) is mocap layered with Walk Designer walks. 

That said, I agree that Poser's IK and graph editor, and particularly its bvh import could use an upgrade, paticualrly the bvh import. I mean, it's just math, right? Why can't it resize bvh data to the skeleton in Poser? A clean import would be an enormous improvement for me, since I spend a lot of time trying to fix foot-skating. Fortuntely, IKinema is working on a web-based retargeting tool that shows real promise, and maybe that will help me with that.

As I see it, Poser is just one of many tools to use for animation, as any 3D package should be. Even those using Maya and other high-end 3D packages use a number of other packages in conjunction, and don't bill themselves as one-stop shopping.