My playing actually improved in BF4 since using an RF87U, and that's coming from someone who used MX Browns consistently.
Could it be that you've just gotten better?
I don't think a keyboard makes a huge difference in gaming for the most part unless you're using one that makes you prone to pressing the wrong key, fatigues you easily, is uncomfortable, or leaves you short of mouse space.
From my experience, Topre doesn't feel very pleasant to game on though my performance doesn't seem affected (except HHKB because of where Ctrl is).