I highly doubt we will get 13 companions. And as such, yes, it is a reasonable concern we will not have enough good-aligned companions to create a balanced good-aligned party.
If
Kevin VanOrd's words are to be believed then: ''They plan to have eight companions, possibly more, and potentially including companions that won't be origin characters
There will be more companions than DoS2 but possibly less than BG2. Part of the "less than BG2" bit is because they want all the companions to have fleshed out stories''
