It will come with time. I'm rarely the absolute best player in terms of fast aiming, etc., on any given server in any given FPS. I like to think I'm decent at the games I enjoy, but as may be, I too had a hard time with BA at first, and trust me, you don't know "hard to kill" this late in the game; at various points in the alpha and even early beta BA were nigh ungodly.
BUT, during the Sunday play tests in early alpha (before public beta was released), every Sunday, every time we played Clearcut, I knew I could count on KitLightning being on Clan and coming down south to camp the exit of our main hangar as a BA, and oh but did epic battles ensue. Eventually, however, as I got better and more experienced, I got to the point where I could kill Kit's laggy-ass reliably at range; since then I still have a tendency to consider each mech purchase based on whether it has weapons suitable for how I play AND whether I can use them effectively against BA.
Trust me, it will come with time.