Well that's not true. You can make perfectly adequate gauss fighters. Low hit percentage is compensated for by the high rate of fire. The size 1 Tryrar mentions was in a quad mount, meaning 12-16 shots. Even at low accuracy you stand a reasonable chance of shooting down a missile or scoring several hits on a larger target. Or you could do a size 3-4 GC and get 3-4 shots at higher accuracy.
I prefer miniaturized lasers myself, but *shrug*
We have very different ideas of "adequate".
First problem, beam armed fighters have to get into extremely close range, in the case of GC armed platforms that is functionally pointblank. This is very difficult since all defenses designed to engage missiles will see fighters at the same ranges and usually can engage said fighters well before they can return fire. Not adequate in my book.
Second problem, whether you install a size 1 quad or size 4 single turret the results are the same. The accuracy penalty is linear. The best that you can reasonably expect is a single hit against a missile salvo or a large ship. Definitely not adequate in my book.
Third problem, the turret in question is quite large for a fighter, 5.44hs for the quad size 1 and 5.6hs for the single size 4. With fighters limited to a maximum of 10hs either system is over 50% of the available mass. By the time you add a BFC, engine, fuel, and minimum armor your over 8hs's which means that the resulting fighter is slow. Again, not adequate in my book.
Let's look at some actual numbers from the game.
For illustration purposes this is the tech available and that some other friendly source has the targets on active scan:
Nuclear Thermal Engine Technology - produces a ship speed of 2000kps for 25% hs expenditure for military engines
Power Efficiency -20%, Power Increase 10%, Exp 10% - above ship speed can change to 2,200kps
Fighter Engine (max one per ship) - (since we're discussing fighters) with power increase a 250ton(5hs) fighter has speed 5,280kps and a 500ton(10hs) fighter has speed 2,640kps.
High Density Duranium Armour - 8 points of protection hs used.
Beam Fire Control 50% Range 24,000 km - standard size BFC has a maximum range of 48,000km
Fire Control Speed Rating 3000 km/s - provides a tracking speed for one tech level above organic ship speed.
Max Tracking Time Bonus vs Missiles 20% - reasonable expenditure compared to other techs, next level is 3x more.
Turret Tracking Speed (10% Gear) 3000 km/s - need turrets to at least as fast as the fire control.
Gauss Cannon Rate of Fire 4 - since the ordinal post specified a ROF of 4 per 5 second impulse.
We can reasonably except to face missiles with a minimum speed of 30,000kps and ship speeds of 3,000kps(one engine tech level above ours)
From the tech above we need these components:
Fuel Storage - Tiny - .1hs - smallest ship mounted fuel cell (capacity 5,000 liters)
Command Module -.1hs - accommodations for up to 20 crew
fighter engine - 1 hs - producing 26.4 points for propulsion.
beam fire control(fighter) - 1hs - std size for tracking speed(fighter BFC's start at 4X tracking speed) and std size for range(needs to fit into fighter) giving a max range of 48,000km/tracking speed of 12,000kps.
quad Gauss Cannon Size vs Accuracy 1HS and 17% with turret gears for tracking speed of 12,000kps - 5.44hs
single Gauss Cannon Size vs Accuracy 4HS and 67% with turret gears for tracking speed of 12,000kps - 5.6hs
When assembled with the quad turret we get at a minimum an 8.47hs(423.5tons/1 layer armor for .83hs) fighter with speed 3,117kps that has 16 shots at a single target per 5 second impulse with a usable tracking speed of 12,000kps and a base fire control hit chance at 10,000km(minimum range) of 79%. With the GC modifier that becomes 13.43% at 10k/km before tracking speed modifiers. Since we looking at engaging speed 30k/kps missiles the penalty is a further 60% reduction to 5.372%. If the full tracking bonus can be applied that is modified back to 8.058% per shot. Out of those 16 shots you can expect about 1.72 hits. Against a large ship we don't do much better since the 13.43% hit chance still only generates an expected 2.15 hits from 16 shots.
When assembled with the single turret we get at a minimum an 8.65hs(432.5tons/1 layer armor for .85hs) fighter with speed 3,052kps that has 4 shots at a single target per 5 second impulse with a usable tracking speed of 12,000kps and a base fire control hit chance at 10,000km(minimum range) of 79%. With the GC modifier that becomes 52.93% at 10k/km before tracking speed modifiers. Since we looking at engaging speed 30k/kps missiles the penalty is a further 60% reduction to 21.172%. If the full tracking bonus can be applied that is modified back to 31.758% per shot. Out of those 4 shots you can expect about 1.7 hits. Against a large ship we don't do much better since the 52.93% hit chance still only generates an expected 2.12 hits from 4 shots.
Neither platform is adequate in my opinion for either missile defense or close attack.
