Well, Battle Rifles are more closely related to assault rifles than they are to longarms. To be honest, the problem with Longarms is that the only weapon class in the skill you're gunbunny is going to be using in most situations is a shotgun. For Street Samurai and Weapons Specialists, there isn't much call for such things.
However, I've found that longarms is a great skill for low-IP characters. Any character that normally has 1-2 IP can arguably be more effective with a sniper rifle or shotgun than they can with automatics. Especially if that character is a mage or a hacker/technomancer. Use a sniper rifle to 'reach out and touch someone' at range, and then switch to a shotgun when people are closer in.
So Longarms isn't that bad, all told, it just isn't good for the primary 'shooter' types. But it makes a great secondary or tertiary role for a character, since there are times when sniping will come up. Just like having someone with Demolitions is nice, even though it doesn't come up too often. (What? Why would giant explosions bringing down entire buildings get the cops to hustle to that location?)
But it is true that the skill needs more love. Look through Gun Heaven, and you see one sniper rifle, one sport rifle, and not a single shotgun. Now I'm not saying we need to pump out a ton of Barrett 121 clones, but new sniper rifles, sport rifles, and shotguns would be great.