That is never stated in the game. All that is said in game about the Aeolus is they're excellent at taking down fighters and that that there were 24 of them made, no reason was given why
only 24 of them were made.
You base that on in-game assumptions. In the Universe the Hecate is far better than the Orion.
The new GTD Hecate class of destroyers is replacing the Orion class as the flagship of Terran battle groups. More heavily armed than the Orion, the Hecate also carries over 150 combat spacecraft and a crew of 10,000. The GTD Aquitaine is a superb example of this new ship class, serving as the flagship of the Capella-based 3rd Fleet.
It says it's more heavily armed, that's it. Far better isn't included in there, only replacing and better armed.
There are several examples of ships being replaced by newer, inferior models in history. The Kirov for example, was a highly impressive but difficult to maintain ship, and only one was ever made.