So what? They're not going to give chase if an attacking force runs away. Given the speed of mass driver projectiles in the Mass Effect Universe, and the claim of relativistic ranges for engagements (without hard numbers though) they can be mobile enough to dodge incoming fire, and that's all that's needed.
They'll be stuck with painfully slow accelerations and no shields, both of which are the main mitigation factors against mass driver effectiveness in the ME universe. This is especially true as the ME ships appear to still be able to manuever to some extent while keeping their spinal mounts on target... a point which becomes completely irrelevant if the fire rate is very low, like on the order of several minutes per shot.
Lack of shields is indeed a problem, making stationary defenses much more vulnerable than ships. This is obviously offset by them being much less expensive than ships.
I don't see where there's anything in Mass Effect 1 or 2 that states the spinal guns can track independently.
Lets say you built a massive, several kilometer long railgun that'd be required to pierce a dreadnought's shielding. Without the eezo required to make the gun as efficient as the dreadnought version, it'd be larger, and without the eezo in the dreadnought drive, you'd be hard pressed to get that massive chunk of metal moving ANYWHERE in short order, let alone dodge return fire. And, again, without eezo, you're not going to be putting on the shielding required to defend against any sort of return fire. The first hit from an opposing railgun is likely to be a kill.
You don't build one that big. While a single shot of a railgun of manageable size might not pierce a Dreadnought's shields, a hundred of them will. And given the availability of resources, a hundred shots will easily come in the first wave of projectiles. The Dreadnought can shoot back, but taking them out one gun at a time is going to take much longer than it can survive the incoming fire. Besides, given the small numbers of Dreadnoughts, they're not the main concern.
In this scenario, the dreadnought that this defense is meant to counter simply sits at a range where it can dodge or absorb most incoming shots, and FTLs out if things go bad. In the meantime, its own railguns are putting out shots that will kill your static defenses at any range that you'll be hard pressed to dodge. It will absolutely clean house... the defenses--whatever their volume--are basically going to be target practice and not a credible threat.
Hardly. If sitting out at range, neither the Dreadnought nor the static defenses are going to hit anything much. The Dreadnought has to stay beyond laser range or be toast (and the static defenses will have much greater laser range) and given the speed of mass driver projectiles in the Mass Effect Universe, even a conservative estimate of laser ranges gives either side plenty of time to dodge. I'd actually say that the claim of the Mass Effect Codex that most battles are fought at long ranges contradicts the descriptions of the technology. In a fight between ships with Mass Effect drives, lasers should actually be the longer ranged weapon since, given the possible accelerations, no mass driver projectile will hit at any distance.
Projectiles aren't a useful anti-Dreadnought weapon anyway. If anyone shows up in a Dreadnought close to a planet, greet them with a few thousand nukes. Shields don't work against those (since they don't work against lasers either) and even one thousand is way beyond the point defence capacity of any ME ship. And it's not even 1% of a reasonable estimate of the arsenal of an average industrialized planet with peacetime defence spending.
Hell, if there's such a thing as bomb-pumped lasers in the ME Universe, you can just mine the space around planets and Relays and blow ships to bits as soon as they appear. Given the absolute necessity of Relays for travel, i'd expect pretty much all heavy defences concentrated there anyway.
As far as I can tell, eezo is really potent stuff as far as sci-fi unobtanium goes. A ship with it is essentially godlike to one without.
It makes for very nice drive technology, though it's hard to say how nice, as there's not actually any data available as to what kinds of accelerations are possible in normal space. But it hardly rises to the level of godlike. Outranging the enemy is nice, but the projectiles in ME aren't actually fast enough to be very effective at high ranges, a laser with a range of a few lightseconds would be significantly more godlike, since it can't be stopped. Shields are nice, but only against projectiles.
Technically speaking, for the same amount of money that can be used to buy a fleet of fighter jets you could mine a country so thoroughly that a fieldmouse farting would set off a chain of explosions. Those mines still aren't a threat unless the fighter pilots decide to land on them.
Mines in space aren't contact triggered.
The volume and scale of the firepower isn't going to be the deciding factor unless a slugging match can be enforced. When the targets have FTL drives, they don't need to stick around for one of those, and their shields make them better able to last through one of those anyways.
Given the incredible difference in firepower, yes, it's going to be decisive. A ship with an Element Zero drive might be a hundred times more effective for it's mass than simple stationary defences, but even a whole fleet is still going to be outclassed a thousand to one on top of that if it goes up against the defences of even a single planet.
The biggest problem is indeed one of volume. No fleet could ever hope to penetrate the laser defence of a heavily defended target. They just don't have the volume to saturate the defences, or the magazines to wear them down.
It is similar to the animal fights the romans liked to stage. You'd think no number of dogs could bring down a bear, because he's so much bigger, stronger and tougher. But quantity has it's own quality if correctly used.
Oh, and the missile swarms you describe would require eezo for the breaching mechanisms, otherwise they'd never get past the shields. And if they were launched from long range, as a static defense would likely be doing, the target would have time to say "screw this!" and jump to FTL.
No, as static defense would not likely act stupid. And missiles don't need to get past shields, as shields only work against objects, not radiation.
