My point is as follows, variants are either upgrades, ie changes that make the ship better at its primary task. Just like the F-15Cs have been upgraded to F-15Es allowing them improved primary task capabilities they had before, plus a ground attack capability. While obsolete airframes such as the F-4 Phantom were used in the Wild Weasle electronic warfare aircraft. The British used old 1950s carrier bombers called Buccaneers as specialized Laser Guide aircraft during Gulf War I.
In the Case of new ships like the Chronos, Marathon and Nemesis they are in the process of replacing the Olympus, Late Model Hyperions and Omegas which are presumably still in service. The models being replaced are given over to specialist tasks such as bombardment (missile), assault or other variants.
Presumably after a the civil war and the shadow wars (and the Drakh War) the EA is in a situation of high production and low availability of resources. So new production goes to high priority areas, i.e. long range ships and cutting edge warships, while obsolete and mothballed ships would be adapted to support roles. The best anology should be Israeli Armour. Where tank hulls go from front line tanks, to support tanks to chasses for self propelled artillery and re-supply tractors over the history of a hull. The Israelis were still using WWII era Sherman and captured T-55 hulls for other tasks as late as the Lebanon invasion in 1982.
Also, the German conversion program to self propelled guns used obsolete Pz-I, Pz-II and captured Czech and French tank chassis for the StuGs, Hummels and Wespe.
So what I am proposing, is that it is more plausable that we find bombardment, assault, carrier and cargo versions of the Omega before they start the complicated engineering task of putting a large laser on a nice 4 AD, B, SAP, TD boresighted beamweapon on a newly built ship one PL above it...
