[JETT] Should I MAX DRONE or MAX GAMMA MISSILE?

If you're thinking long term, I would max Drone Blast over Gamma Missile. It does more hits per second than Rapid Fire so it's stronger if you hit the damage cap. Gamma Missile is just for mobbing purposes anyways.

Solar Array does get outdamaged in 4th job by Suborbital Bombardier but it still has much better range. There might be situations where Solar Array can hit platforms that Suborbital Bombardier cannot.