It's difficult to quantify "what Biggs should cost"
because his true cost reflects both the durability and the damage output of whatever he is protecting.
Because Biggs exists, from a game design standpoint there are strict upper bounds to what rebel ships can be allowed to do while retaining balance. For instance, a group of Phantoms protected by Biggs would probably be disgustingly overpowered.
Every future rebel ship design needs to keep Biggs in mind. Hence, he warps the design space.
That's my interpretation at least.
Edited by Introverdant