I personally think that giving Osiris the Trebuchet was a great move.
I play this deck:
6qq 6qq 6qq 6qq 6qq 6qq 6rn 6rn 6rn 6rn 6rn 6rn 6u3 6u3 6u3 6u3 6u3 6u3 6u6 6u7 6u7 71c 74b 77i 77i 7dm 7gp 7gp 7js 7k2 7n3 7q0 7q0 7q0 7q5 7q5 7q5 7q5 7q7 7q8 7t9 7t9 80h 80h
All in all, a reasonably standard rainbow that has Anubis and Aflatoxin with the noted lack of a second Otyugh. Obviously, Aflatoxin is going to be great, Miracle is really good, SoGs are absolutely necessary. My first game against Osiris was fairly average as games go. He didn't draw his third Trebuchet until I was almost done drawing off 1 Hourglass and he was at around 25 cards (I stole an early Eternity). My life total went way down to around 10 before I used a Miracle because I didn't draw Anubis until my fourth last card and couldn't get the main mutant combo set up. My Aflatoxin came when he had about half the field filled. Nothing was too optimized.
Now obviously I see what could be worse. He could have had a third Trebuchet, I could have failed to get Miracle in time. I could have drawn Aflatoxin quite a bit later. But along the same vein, everything could have gone even better. I could have gotten an earlier explosion and taken down a Trebuchet. I could have stolen a Trebuchet instead of a second Eternity (Didn't think it was necessary, thought he only had 2). Anything I could have drawn later I could also have drawn earlier. It's all quite chancy and Osiris is obviously harder but let's face it, all FGs should have a bit of luck involved.