Adding a normal 6cm laser could make early to mid game point defense too strong. Depending on stats they could compete with medium level gauss cannons for best point defense beam weapon.
A 6cm laser would deal either 1 or 2 damage. At max tech (i.e. range multiplier x12) a 1 pt laser would have twice the range of max tech gauss, but fire only one shot compared to 8 for gauss. Suppose 6cm lasers weigh in at 2 HS. Further suppose it has 50% size reduction but you can still achieve a 5 sec firing rate with max tech capacitors. So 1 HS, 1 dam, 100% accuracy. Six of these has the same size as a 6 HS, 1 dam, 100% accuracy gauss cannon. The difference: gauss gets 8 shots, laser gets 6 shots and double range (still useless for anything but final fire). Without 50% size reduction, the laser only gets 3 shots for the same hull space. So gauss remains the superior PD choice (since both deal 1 damage, missile armor doesn't matter).
If the 6cm laser dealt 2 damage, it'd give gauss a run for its money at 2 HS. IIRC 10cm lasers are only 3 HS, so a 2 pt laser would need to be 2.5 HS or 3 HS for balance. At 3 HS, why bother? At 2.5, you don't gain anything substantial, so again why bother?
So no, I don't think there's anything to be gained by adding smaller lasers. They certainly wouldn't outperform gauss on the PD front.
On the agility what if fighter and gun boat engines gave the ship an agility rating. It could either reduce the hit percent like ecm does to beam weapons but for all weapons or be a multiplier to the speed in the chance to hit formula.
I think agility/maneuvering is already implied in the "speed makes you hard to hit" calculation. If gunboats/fighters need an extra dodge bonus (and IMO they don't), their size should be the reason. Maybe add an accuracy penalty against ships below a certain size? That size could be, say, 10-20% of the firing ship's size. But then specialized anti-fighter turrets/fire controls (you know, with high tracking speed) would perform poorly. This would also make PD horrible, since missiles are in some sense tiny ships (20 MSP = 1 HS).
Personally, I'm satisfied with the way it's handled now. Fire controls with high tracking speed are heavier and probably don't have the same range (since range and speed scale independently, and you probably don't want 16 HS fire controls). Your tracking speed is the minimum of your FC and your weapon. Standard weapon tracking speed is the maximum of ship speed (high for GBs/fighters) and base tracking speed tech (the FC one, not the turret one -- either way, it's poor against GBs/fighters). Turreted weapons with high tracking speed are heavy. So full size warships shooting at small craft have heavy weapons, low accuracy, or both.
The only defense a fighter needs is high speed. I like the OP's suggestions here: x5 mult instead of x3 and/or no engine limit. They make fighters more competitive against GBs speed-wise (but not firepower- or armor-wise), and heavy fighters (10 HS) become viable. GBs/fighters do
not need a magic agility rating to add moar evasion. Remember: They're cheap and quick. Cheap means they shouldn't match a larger ship's firepower and durability. Quick means they're great for pursuit, harassment (hit-and-run), and keeping your larger, more expensive ships out of harm's way.