Carriers are highly efficient in terms of mass/logistics. You can invest 90 mass (i.e. 1 large ship) into getting 3 small assault ships, which can use 150 mass on their own (or use 7 logistics to get 9). This is before any boni. With boni you can do stuff like getting a huge hull with 5 modules, i.e. you generate 15 assault fighters (45 logistics) from a 10 logistics ship. Or in terms of mass: invest 337.5 mass (assuming you took the 25% support bonus after interstellar travel) and gain 15x50x(1+capacity boni). Assuming the capacity noi add up to 1 (with thalan I usually end up with 1.5, without hyperion shrinker), you get 1500 mass out of 337.5 mass.
The thing they changed a while ago, is that fighters do not instantly repair/replace between battles. Which is very reasonable.
Another aspect is, that large ships do a lot of overkill damage to small ships, e.g. your 300 beam damage capital ship shoots a 50 hp, 8 shield point fighter twice to kill it, when it could kill a 150 shield 300 hp ship in two shots instead.
With AI Tweaks it is a very different story, because there is nothing, that stops assaults from just focussing down all support ships (carriers). In the normal balance you add a couple of escorts to your fleet, which have nothing but defense on them. they will stay with the carriers and be attacked by everything before the carriers.