Wait, so Estates go straight to Curses, as does Copper. And actions(including Catapult!) go to cheaper actions or Curses... Seems a little too strong, somehow. And for each Catapult too. Chapel Catapult would be awful to face at 3-4.
e.g. Chapel Catapult, T3 Chapel 2 Estate 2 Copper, T4 Catapult Estate 4 Copper buys Catapult 2 and Engineer, T5 Catapult Catapult Engineer Estate 3 Copper buys Catapult...
and if they hit your Chapel or Catapult you're pretty much out.
I don't think Catapult necessarily needs $1 on top of the attack; Market only gives +Buy on top of that and still costs $5, and I'd say the Engineer attack in most situations is better.
Catapult doesn't have an attack, it's just a $5 Peddler that gives you the option to gain an unreliable attack card with no self-benefit. Its strength is questionable. Consider:
First, you need to match up Engineer with a Catapult.
If Engineer hits Copper or Curse, it's strictly worse than Swindler since it doesn't give you +$2. If it hits Estate, the attack portion is only a little better than Swindler. You downgrade their Estate, but this usually doesn't matter either way. Junk is junk.
Hitting Silver is decent, since it downgrades to Copper.
Hitting $3 actions might hurt the most, because it will often go Curse... but not if there's an acceptable $2 on the board.
In the end, Engineer is just a mix of Swindler, Saboteur and Knights. The best case is if you can set it up to have just one Engineer in your deck firing multiple Catapults, but the attack is still unreliable. It trades off some of the trashing attack power (reliability of Saboteur, unmitigated destruction of Knights) for the possibility of Cursing, and it's definitely not as strong a junker as any of the actual Cursing attacks.
The scenario you describe with Chapel/Catapult requires drawing Chapel with 2 Estates on turn 3, which is near ideal. The same situation with Witch, Mountebank, Cultist or even Wharf or a Knight is probably just as good.
It might be overbearing, but I don't think it's obviously so.
