The Javelin has a medium sized hangar, and you also seem to have forgotten about the Kraken, you know, the one that can carry 8 fighters not 3, the one with the tiny crew compliment compared to running an Idris?
The one with the S8 STS turret on the nose that doest require you to line up your entire ship to get a shot off.
That Kraken,
But as I said, fighters in capital ship battles will be next to worthless.
No I didn't forget about the Kraken that is a really good fleet carrier... but all the ship will be sitting into an open pad, not enclosed within the ship, and that in a combat scenario means open to enemy fire in addition to have to carry out R&R operation while in EVA sistuation. Will the kraken shileds protect them? at to what extent (balistics weapons still bypass a good amount of shields)?
About the Javelin yes, it does have a medium size hangar but it's suitable for only one ship and, as I state before, can't land on planet, so it fill a different slot in several situation.
I'm not saying that the Idris is superior to other ships, but it has his own place and there are situation where the idris will be a better choice compared to other similar or more capable ship.
Will it be the go-to choice? No, but as long as we have the ship into gamers hands and a game's state that allow different enviroments' situations I'm not going to consider the Idris a pile of junk.
Another aspect that neet to be taken into account, other then rough specifics, is ship survaivability: how armor is gonna work? How renduntant will the system be? On pure speculation I don't see a ship like the Kraken have a better survivability the the Idris in higth combat enviroment for example and that could lead to have the whole ship and his cargo holded away for repair not to consider the costs...
As I sayed too many factor to be considered, most of them are related to game's content that are not out yet.