The reason scatter volley makes FAW obsolete has nothing to do with its duration and everything to do with the facts that
1.) CSV is very directional and selective with targets = more damage per target. FAW shoots at everything within, at minimum, twice the radius and at maximum a complete sphere.
2.) CSV doesn't castrate your power levels and reduce your weapons to the status of nerf guns. FAW does.
You are missing one important difference. BFaW is intended to be used with beam arrays and beam arrays are the tipical weapon of cruisers. Cruisers are not attack ships but support ones and BFaW is very good to hit pets, torpedo and mines all over around the cruiser in a 10Km radius with no need to target the object... a good defensive ability . Moreover a cruiser can use it to get the agro and protect the others ships from being attacked.
CVS is intended to be used with cannons, the tipical weapon of an attack ship. CSV is not intended as a defensive ability but an attack one... a massive attack to multiple target in front of you...
the difference between BFaW and CSV is the same difference between cruisers and escorts: 2 abilities 2 roles <-> 2 ships 2 roles
If you think that BFaW and CSV have the same role, you do not have undestrand much a