Well, I built a few fighters, and they're trully amazing in small scales battles (I'm in the 7th scenario).
To attack a planet, I have one capital ship (with bombers), around 20 lights fregates, 2 repare ships (i researched) and 5 carriers (8 fighters & 2 bombers) and that's more than enough usually against a normal CPU.
I focus fire on capital ship with bombers and capital, kill small frigates with my lights one and harash LRM/fighters with my fighters, that's does works.
I never used squadron, but they trully are a non-negligible force, thx for the advice !