I think I'll have to run the numbers again, let's see...
2 million health
1.5k dmg each
50% of my shots hit, so 750 average damage, so 2.6k shots, that's 133333 honor, plus 500 honor to purchase the weapons, let's say we purchase 50, that's 2261 honor each. Certainly not outside the realm of possibility. I think if we had prepared for that strat and knew ahead of time we'd be able to successfully get the scroll it's possible we could've farmed enough honor to get it.
But even if you destroy the gatehouse you've still got a tough road ahead of you, but not impossible.
The two big changes that would make it more reasonable would be:
1. Add an increasing respawn timer so you can't just respawn and run in.
2. Make it such that trebs need to be damage by other siege weapons or mines or whatever and can't just be taken out by by a few players.