The main problem is its heavy expense for what it is- if the SV had a really good ace, it would be different. If you want to see a similar effect- see the problem of the generic T-70s. The T-70 is good, but it's a Poe Dameron/Red Ace carrier, the same way the E-wing is a Corran boat.
I'm not sure I follow you there. The E-Wing *isn't* good, but Corran is good enough to make up for the handicap (or at least that's the received wisdom). I don't know if the same is true of the T-70. Is that what you're saying about the Starviper?