I think the fundamental issue with x7s is the low skill floor combined with high performance. The x7 Defenders are not only good, they're good despite the pilot making mistakes. Bump a ship, run over a rock or debris, take stress from fire ... you still get that token, and at a point reduction to boot.
They're beatable, certainly, but shouldn't be essentially immune to player mistakes.
One simple fix: make the evade from x7 a free action, not a free token, and they come back into balance. They'll still be very good, but they can be countered, and if the player makes a mistake they still pay for it.