The pinnacle of GTVA technology, nothing and no one (smaller than a destroyer, anyways) is superior to the Erinyes. Pilots used to having lots of missiles in a heavy fighter will be somewhat disappointed, but the Eryines does have more missiles than the standard GTVA fighter. Those eight primary cannons, however, are truly impressive in their destructive power. Unfortunately, the Erinyes mounts a few too many guns for its capacitor to handle on mid-to-high difficult levels and so should mount a mixed armament, unless one is an expert marksman.
This ship is good for all purposes, whether they be attack or escort. The secondary banks are somewhat small for a vessel its size, but greater than most and especially compensated by its enormous firepower. Getting hit by a full bank of Prometheus S will put anything in bad shape, especially considering how close the shots are to each other, which means that it is not likely you will be hit by a glancing shot. However, repeated firing will drain your power supply quickly. It also has lots of armor, good maneuverability and adequate speed for a heavy fighter, and a small target profile when viewed from the front and back, though it can be easily hit from the sides.
The real advantage of the Erinyes is its versatility: it can mount nearly every non-bomb weapon. Sure, most ships can do one or two things better than it can, but it betters every one of them in at least one useful respect. It's the only 'Everyman' Fighter in either game not to suffer from not being able to mount some of the better ordnanace, and nothing chews through entire Shivan bomber waves quite as fast as close in primary fire from an Erinyes.
Fans tend to overrate the Erinyes's specifications and regard it as undefeatable and indestructible simply because it has 8 primary banks. It is doubtlessly an advantage, but every advantage has a disadvantage: The Erinyes eats more primary power than any other fighters in the game. In addition, it is slow, unmaneuverable, and easy to hit even from long range. While a skilled pilot is able to survive an attack from behind, the Erinyes still rates low on survivability due to its large size and sluggishness. Although its weapon compatibility is excellent, anti-cruiser and anti-warship bombs cannot be mounted on the Erinyes. It's pretty suitable for escort missions as long as proper fighter escort is given to take down any interceptor fighters that might attack the escorters. With its firepower, taking down bombers is easier than with any other craft, but in order to maintain a pauseless flow of laser, you must divert more power to your primaries. This usually means slower shield recharge or even less speed; or usually both. Its disadvantage in escort missions is its low speed, which is rarely compensated by its superior primary firepower.
There is little need for Prometheus or Kaysers on this. 8 Subachs can do serious damage and be fired continuously, though some additional stopping power could be supported, if that is your choice.
I wouldn't be too mad over the Erinyes' small secondary banks; just fill them up with Tempests and be done with it! The fact that the Erinyes can be mounted with almost any gun available to the player means that there is almost no need to have aspect-seeking missiles.
Although I personally prefer the GTF Ares when I need to use a Terran ship, The Erinyes is a close second; not just because of the sheer number of gun ports, but because of their arrangement. The guns in the first bank are perfectly arrayed for high accuracy at close to medium range. I usually put my anti-fighter gun there, and then put my anti-cruiser gun in the slightly-less-accurate second bank.
As mentioned above the Erinyes is often overrated with its raw firepower. However this ship is hardly the most manueverable thing in the GTVA hangars, and needless to say far from fast. With its subpar handling I would not want to dogfight in this thing, so logically anything with a shorter range than the Prom-S would be out of the question. If you cannot snipe it, get someone else to kill it. The Erinyes is a ship I would avoid flying in hard mode, especially in the last two missions. Dragons will chew you up real quick.
The Erinyes does indeed depend on its primary loadout more than other Terran fighters. However, I have never had a problem with maneuverability. Top speed is about the same as a Herc II, but it is far more maneuverable, and the combination of Subachs and Kaysers as primaries can alleviate energy-management problems. Dogfighting in an Erinyes will typically be just a matter of getting the target in your sights for a just few seconds, then letting fly with full guns. Nearly all fighter craft will die very quickly from a few Erinyes salvos, even the above-mentioned Dragons, while the shields and hull are strong enough to keep you in the fight long enough to come to bear and proceed onwards after. My preferred fighter for the late-game missions on Hard, with the Perseus taking second.
The Erinyes is a good heavy fighter, it has the exact same maneuverability as the Herc II, and is slightly faster, but has significantly lower survivability due to a reduction in shielding and increase in target size. It's salvation - the primary firepower of eight guns, is significant. If one has need to quickly engage and destroy wing after wing of the ridiculously well armored Nephilim and Seraphim bombers on Insane, there are few fighters that are better to take. Although the Ares and Myrmidon approach it in firepower, they fall short in speed and survivability respectively.
Against fellow human players, in relatively even fighter versus fighter engagements, is where the Erinyes can truly shine. Its eight primary banks arrangement allows it to deliver accurate and deadly fire on approach, discouraging opposing fighters from challenging your approach for fear of being pulverized, thus making it easier to close in. It has the potential to stand toe to toe against any fighter and come out on top. Although it might lack qualities for some pilots to consider it one of the best fighters, it's not to be underestimated. It's extremely effective, and dangerous to face.
Against AI opponents, it's devastating. Its eight gun mounts, good all around stats, and access to the majority of weapons in the game allow it to be effective in a lot of situations. Need a fighter to hunt Shivan fighters in a nebula and kill them quick? Mount dual Kayser and Tempest and have at it. Need a fighter that can finish off cruisers but also defend against and quickly dispatch bombers? Slap on a Maxim paired with the Kayser/Prometheus-S and equip the Trebuchet.
It's worth noting the Erinyes' potential as a ship-killer--equip one with 8 Maxims and some Trebuchets. With the 8 Maxims alone, based on shorthand calculations, you can deal almost 1400 damage per second, from 3000+ meters away (well outside the range of almost every anti-air defense a capital ship has). From that same range, you can launch quite a few Trebuchet missiles at turrets and subsystems of your choosing (in addition to some extra damage to the hull). At closer range, employing the use of Infyrnos (which, thanks to their dumbfire nature and fast speed, work quite well with this kind of build) can ramp up that damage to absurd levels. A wing of Erinyeses equipped like this is a major threat to a corvette, and with two wings, a destroyer. While it would definitely still require fighter cover (unless you equip Tornado/Harpoon/Tempest missiles in your secondaries instead), they would be leagues faster than even lighter bombers, still quite durable, and still decently maneuverable. However, do not underestimate the power of 8 Maxims even against shielded fighters--a sustained burst can still tear down your shields, and your hull would follow in very rapid order--so don't let one get a bead on you.