In Starship of the Line, the rules set analogous to High Guard I'm developing for use with T5, I have a place for fighters, torpedo boats and frigates. Specifically, that is either at close range or in the screen formation.
(In Starship of the Line, task forced burn maneuver Gs for maneuvers and to enter formations. A weapon's ability to penetrate armour is represented by its penetration + damage; once it penetrates, damage is applied to individual systems.)
Close range is near-visual range for starships; in Brilliant Lances, it would be less than one hex (30,000 km.) At close range, a task force doesn't get any bonus for evading (+1 difficulty to hit for 2 maneuver Gs, i.e. a bargain) because the range is so short their velocity won't move them out of the way quickly enough. (Missiles launched at close range also ignore evasion, because they have plenty of fuel to burn to catch up.)
At close range, energy weapons are deadly. They'll easily puncture any but the most heavily-armoured hulls. Even a single basic plasma gun will have Pen +4 Dmg 2, being able to fully penetrate factor 5 armour.
The answer to this is the screen formation. A task force that assumes the screen formation must spend 2 maneuver Gs and designate at least half of its ships as escorts. The remaining vessels are escorted. Escorted vessels are never treated as being at close range to an enemy task force, even if the escorts are; use short range penetration and to hit tasks instead. Furthermore, escorts may fire lasers and energy weapons twice at missiles targeted on the escorted ships. If enough escorts are disabled (unable to move or unable to fire) that they can no longer screen the escorted vessels, the formation is broken and no longer applies.
In other words - letting plasma-armed gunboats or missile-carrying fighters near your battleships is a Bad Idea. Protect them with laser-armed frigates. Of course, other formations are equally tempting...like battle line, which allows spinal mounts to fire at reduced maneuver G cost, and echelon, which prevents a task force from being outflanked on one side.
--Devin