Essentials: Crusaders + Guardians + Fighters (fighters will counter repulse and illums) + (Shield repair and malice)
1.Heavy cruisers are primarily designed to take a beating so as to stay alive long enough for repairing to take place. If you gonna spend a hell of amount of money why don't u purchase guardians as well to take away that 33% of damage done to your ships and a handful of drone host with fighters.
2. A fleet of illums is more than the equivalent of a fleet of 100 light frigates with malice turned on. why? well because the illuminators have side beams so in numbers while u focus fire there tearing your fleet apart firing at every ship they can get an angle on.
3. Solution: A mass of Crusaders needs Guardians and mother ships in your case packing malice and shield regen, carriers, Halcyon with fighters and push. How u micro the abilities is up to u. Cost is obviously meaningless to u since u can afford 125 units ! I only add 50, full armor, full shield upgrades with 18 guardians and 3 mother-ships, 2 halcyon , 5 carriers with fighters and i did ok vs a horde of a Javelis fleet.
Malice will take care of your focus firing problem and fighers will take care of u and his illums. Against many illums would i have survived? Dont know but i was bent on surving a beating so i probably wouldnt have lost miserably. (i think i would win )
Honest truth.. doesn't matter how u see it. advent is lacking something in every fight in this game.
Fleet composition is the key and the guardian is the key- the most powerful cruiser its class.