No, this is an honest question. I see two reasons to not use them. Armor is the better choice, to me at least.
Rocket Fighters: With many at 4+ speed and 12 shield penetration, shields drop fast. One can counter with tractor beams, anti-fighter missiles, and such, but that’s costly.
Only 1 frigate weapon has under 10 shield penetration: the Pulse Laser. However, only 6 (out of 11 (12 counting tribe)) have more than 20 armor penetration. At 21 armor, you have just 4 weapons.
A shield resistance of 7 or so just doesn’t cut it.
The shield 2 has 10 resistance, which blocks laser fighters, that’s about it.
Also, 2 armor frigate cost 22% more than 1 shield frigate.
But then, in a sad way, frigate can never beat fleets with dual rocket fighters, regardless of their armor. Cruisers tanks will simply outlast them as they get crit to death. Might as well maximize their effectiveness against laser fighters instead.
People complain all the time about Frigate survivability. I just dont understand it. I never have a problem with them surviving outside of a swarm of dual rocket fighters or a rush of Ion or CL cheese fleets. I usually have them behind my main line cruisers which always have at least 1 scrambler. My Frigates have on average 2 Plasmas, 1 Ion, and 1 SF Missile, along with 3 power armors (regular) and 1 Shield 2, and they last quite awhile, usually longer than the cruisers behind them. I’ve found that 3 power armors doesnt make them immune to fighter weapons, but it makes them highly resistant to them, and the Shield makes them difficult for laser fighters to pick apart. Another thing is that if a frigate is hit by the odd Plasma round, the shield will likely eat it and regen before it gets hit again. Try to have your frigates survive a fighter onslaught with and then without shields.
You already listed so many ways to counter them… Stationary frigates behind cruisers only work if your enemy is
Not rushing
Not using dual rocket fighters
Not have beam lasers that prioritize frigates
And after all that, when you stack a plasma frigate with that much armor and shields, they deal less damage compare to a plasma cruiser with similar credit count.
A Tribe Utopia Plasma with 3 plasmas, 2 beams, a scrambler, a CL, a pulse, and a light shield only cost 1904. (okay Tribe is OP, but)
A Rebel Fenrir Plasma with 3 plasmas, a scramber, a CL, a pulse, a shield 2, and an ultraheavy armor only cost 1721.
And then you look at the armored and shield frigate, which is well over 1000 credits, and doesn’t deal half the DPS.
The point of having some heavily armored or shielded frigates is so they draw fire away from the frigates which have 6 hard points or 8 hard points and absolutely no defenses.