Off-hand, the B-wing (in new canon) was originally to be a space superiority/multirole fighter. But the production version shifted to ordnance-based armament, relegating it into a Y-wing replacement. It wasn't that originally, but became one.
The Assault Gunboat indeed resembles the final B-wing in function (mix of lasers, ion cannons and ordnance), though since the new canonization i still vague (and whether FFG actually recanonized it is debatable since their SW RPG canon status hasn't been clarified, Wookieepedia treats it as canon for most part), they can change still i suppose.