I would say that they can work, though I spoted some strange things.
The Iron Duke has a FC with a tracking speed of 1250... I think you did something wrong when you designed that one and just missed it.
Over all I think your ships might be a bit slow for Ion tech. In general I view each engine tech with a standard engine at 25% of the ships total weight to be the base line speed of ships. For Ion tech this should be 3000km/s. In my opinion most ships military combat ships engines should be between 25-33% of their hull space. If you go lower you should increase the power multiplier to compensate some to get at least to the techs base speed.
This is obviously not law or anything, just what I prefer.
When it comes to point defense then Meson cannons are usually regarded as a good choice as are Lasers and Gauss cannons. If you play against the AI I doubt that they use armored missiles which is where Lasers and Mesons shine the best. Gauss cannons need at least three shots to be better than a laser on the PD duty. Lasers are also good because they have much greater range and can be doubled as anti-ship weapons as well. Gauss cannons are not as good and Meason have relatively lousy range in the early tech eras, but otherwise are good in combat.
When I create a point defense turret of Lasers (which are the same wight as a Mesons) I always put them in quad mounts. In general, when looking at the cost, fire controls are very expensive. I usually view two quad PD turrets (or one Gauss in quad) to be an effective PD system over all. They should have about 50% chance to bring down a same tech missile per shot.
The total weitght with a lased PD defence battery on my ships are generally about 1200 tons and have the potential to shoot down on average about 4 missiles at a reasonable cost in production.
In general Gauss guns are much better as you go forward as PD on your ships and don't neglect CIWS systems either. I always put one or more CIWS on bigger ships such as ships above 10000 tons. As far as my experience goes the AI don't use armoured missiles (but don't quote me on that) and as such Gauss guns is the best final defense PD system you can have.
You might also look at you engine design. Can you make them bigger and save on better fuel efficiency. There might also be different opinions on the amount of fuel you should keep on your ships. I generally don't keep more than around 20 billion range on my bigger capital ships and slightly less on my escorts. I rather keep the tanks on civilian tankers. around 20 billion range is enough for battle maneuvers most of the time. It would also save you some space for more combat goodness.
Another thing I note was your lack of armour on your ships. I never launch combat ships with less than four amour strips unless it is a very small escort or scout, then it is a minimum three layers of armour. A cruiser with less than five armour is rather weak too. That is the type of armour I put on destroyers at about 6000-10000 tons, Cruisers get more.
I always find this worth wile unless you intend to totally smother the enemy with AMM and never close to beam combat, then you might be able to afford low armour on your combat ships.
