I'm sorry guys but you are repeating a bunch of myths and mistakes about WW1 and modern warfare vis-a-vis fortifications now.
It really bears mentioning that artillery in world war 1 could reduce fortifications just fine
No, it could not. It could only destroy old forts, the ones built in the 18th and 19th centuries, but more modern forfications that used domes were almost invulnerable. Shells were generally very underpowered and fuses were unreliable. Gunnery firing arcs were parabolic (not sure that's the right word) and meant that impact angles were low, not high. And of course, calibres were generally relatively small as well. Shells would only graze domed fortifications and bounce off, directing the explosive power outwards.
generally speaking infantry had to abandon their trenches and then try to come back and defend whatever was left after the bombardment
Misleading and only partially true. Infantry would generally take shelter in pillboxes and bunkers during bombardmend, to reduce casualties even further, but the trenches - once they were chest-deep - were good enough to cut down casualties by themselves massively because the attacker basically needed a direct hit on a manned section of the trench to cause any casualties. Even in WW2, when timed fuzes became common place, airbursts weren't reliably hitting inside trenches. Once the bombardment was over, the defending infantry would swarm out of their shelters to man the firing pits, bringing machine guns and light mortars with them, and the trench lines were usually intact. Because again, you needed a direct hit to get it to collapse, and even then the infantry could use the resulting crater as cover.
Later in the war, the Germans started using the Tripwire-method, where the first trench would always be lightly manned and reserves would be brought up to actually defend the second and third trench lines, which I think is the source for the confusion about how it worked.
It makes logical sense for fortification level to degrade due to intense fighting though. One infantryman manages to toss a satchel charge through a gunport, suddenly the pillbox is gone and your fortification is strictly less than it was before. And you can't really rebuild it in the middle of combat, so its gone for good.
Not really. The satchel charge is not going to destroy the pillbox. Sure, the gun is wrecked but defender can easily bring up a replacement gun. Maybe not for some heavy coastal gun, but anything smaller is replaceable. Field fortifications were rebuilt during combat all the time. In both WW1 and WW2 we have thousands and thousands of examples of attacker gaining control of part of the fortifications, only for the defender to counter-attack and then resume defending the original line. Fieldworks can be repaired/rebuilt overnight with only shovels, crowbars and pickaxes.
attackers can still drive defenders out of their hardened structures, thereby capturing an opponent's fortifications, thereby reducing the enemy's level of fortification
Not completely true. Unless the attacker manages an actual
breakthrough, instead of the far more common
break-in, the defender will have a good chance of regaining the position through counter-attacks. The attacker can be subjected to enfilading fusillade from multiple directions while the defender brings in reserves and then throws the attacker out. Every
Which is why I'm advocating that you need special troops to combat fortification levels in Aurora. Because they are a mixture of terrain and construction, basically everything is abstracted into them, from camouflage to natural formations to field works to reinforced concrete (neutronium-duranium?) fortifications, the game shouldn't allow the attacker to wipe it all out "just because".
