That is what I'm thinking too. Add challenge and increase adv cost. It is easier than adding a reduced auto-fire damage mechanic - although I can see that being a good idea too - except it might not make sense. Unless you could agree that the repaid energy cycling does decrease the power in each blaster bolt… it adds math though (or auto-fire setting could get a number after it, similar to stun grenades - which becomes the auto-fire damage). That way you could easily keep it at 1 advantage, add challenge die and say as a default that auto-fire decreases the based damage by 4 or 3 or something. Heavy blaster rifle could have auto-fire 6 or 7 - so it still packs a punch, but not nearly as bad.
Although I am more keen on the increased advantage cost and challenge die addition.