1) Units always have at least 1 attack. That was one of the proposals the testplayers group agreed last time we discussed the rules. I don't know how official those changes were but we are playing according this rules in tournament (not that this would have saved the Gyro of course :-)
2) One stand units are never as efficient as standard units. Look at the Steam Tank, Bone Giant, Sphinx, Chaos Spawn. The Cost/Attack/Hit Points ratio is never as good. That's part of the philosophy. But beyond that changes are of course discussable.
The Gyro is no flying tank, there's a good reason why it uses a steam cannon (weight?) and to give him a 4+sv or to even make him defended is imo not the way. But it could be interesting to just give him a few more hit points so his chances to survive the first round of combat is a bit higher. And as a flyer (with a good 5+sv) that could save his life. 4 Hit points should not be any problem, 6 maybe would be a bit daring. Opinions?
Greetings,
Gerald