I considered that point on slugs as well, but currently there is no technology (in real life) to intercept artillery shells as far as i know?
In principle, intercepting an artillery shell is no different from intercepting a missile, and were it not for the difference in the size of the target might even be easier; most artillery shells are, after all, incapable of adjusting course mid-flight and follow highly-predictable ballistic flightpaths. If you know the velocity and location of the shell at some point in time, you can predict where it will be at a specific point in the future with a fair degree of accuracy. The problem is that it's a very small target, which makes it very hard to determine its velocity and position with sufficient accuracy to intercept the projectile and also makes it difficult to aim the intercepting weapon with sufficient accuracy to actually hit the projectile assuming that you can compute an intercept solution, and on top of that the projectile is moving fairly quickly and in all likelihood wasn't all that far from its target in the first place, meaning that you have to do all of this quickly.
That being said, there are already systems in existence which can detect artillery shells and determine their flightpath with sufficient accuracy to know where they came from well enough to bring counterbattery fire into play without needing to actually detect the artillery piece that fired the shell.
Obviously missile defense has no logical reason to provide any defense to beams
Consider what some of the missile defenses that the game uses actually are. Chaff is a cloud of particles intended to distract the targeting of a missile; such a system could perhaps scatter or absorb enough of a beam's energy to reduce the damage that the beam can cause by an amount that matters, though it's not terribly likely to stop the beam completely. ECM is simply one or more of a variety of methods of playing tricks with whatever detectors are in play to throw off the guidance systems of a missile; if the ECM is strong enough, there's no particular reason why it could not be used to throw off the aim of the guns or beam emitters of an attacking warship and thereby cause the attacker to miss, or at least not hit the target as squarely, and thereby reduce the damage caused by the attack. Point defense cannons can potentially function in much the same way as a cloud of chaff could, though I'd tend to favor the cloud of chaff for actually reducing the potency of an incoming beam. Point defense lasers would be completely useless against a beam which was a true laser, though they might be able to do something against the confined-plasma type of sci-fi energy weapons. Aside perhaps from the ECM, most of this probably wouldn't work well, but some of it could do something (I wouldn't really count on the ECM since, at least in GCIII, the evidence is that the ECM isn't good enough to fool whatever detectors are used by ships, just the detectors used in missile guidance systems, and if the missiles are guided by the launching ship rather than by an on-board homing device the method of ECM in use may just be some form of jamming targeting the guidance signal).
Kinetic defense should not even exist,,, it should just be hitpoints - you have stronger amor = more hitpoints.
This is somewhat variable and dependent upon just how strong the armor is relative to the weapon being used. If the weapon I'm using is a 0.50 caliber machine gun and the armor I'm up against is the main belt armor of an Iowa-class battleship, then no, armor is not simply 'more hitpoints,' at least not on any practical timescale (this is a bit of an extreme example, but it gets the point across - it is possible to make armor which is so strong that insufficiently powerful weapons will simply not cause any real damage to the armor or to whatever the armor is protecting on any reasonable timescale; by the same token, armor which is so strong that my 0.50-cal machine gun cannot hurt it on any reasonable timescale may provide about as much protection as wet tissue paper against some other weapon, such as a 16" naval rifle).
Granted, GCIII doesn't make this kind of distinction, and GCII only kind of did (if ship A had 30 effective armor and ship B had 30 or less mass driver attack, then the expected mass driver damage dealt by ship B to ship A was about 0), and of course none of the games in the series really pays any mind to the fact that a tiny ~10m long fighter probably isn't packing any guns which are as powerful as are on an ~800m dreadnought, even if both ships make use of equally advanced technology, at least not if we're talking about 'traditional' guns.
Similarly, Proton Torpedoes work just fine against shielded things in Star Wars.
With the caveat that missiles/torpedoes bypassing Star Wars shields is much more of a video game and stories thing than an actual movies thing. Torpedoes were used against the Trade Federation Battleship in the Phantom Menace and failed to penetrate the shields, and the only time in the original trilogy where torpedoes are known to bypass shielding is against the first Death Star's exhaust port, which was explicitly not protected against that kind of attack.