Standard unit counters. Light Frigates are strong vs. Ranged Frigates--if you're TEC, use Cobalts, if you're Vasari, use Skirmishers. If you're far enough advanced, use Kodiaks or Enforcers, respectively. Advent ships are rather weak when they don't work with other ship-classes, so any spam-fleet is easily dealt with.
You couldn't be more wrong.
Any spam is quickly dealt with. Mixed fleet is invariably better. Against Illuminators, i suggest that you remember that Javelis = 4fleet supply, and Illums=6 and are also much more expensive.
Here's what i go with by the time i have research for my second capital and tier 1 fleet supply
25+ LRM
9 Hashiko
1 Kol
1 Marza.
With hashikos healing units as Illums damage them, you'll be surprised how efficiently you'll defeat his fleet. Illuminators take a bunch of time to kill hashikos.