I don't think that beats Steward+Squire+money. With a bunch of Copper and no draw, you're not going to have an easy time lining up a 3 card combo.
I think you're right, but note that MV+Steward is theoretically a playable draw engine, enough to get a handful of each component into your hand all at once. Maybe unopposed you could get super-thin, play+trash 10 MVs, play 3 Stewards for draw, and use your remaining 8 actions on the 8 terminals in your hand. Something like two Squires for +6 buys, three Coppersmiths, and three Beggars can get a pretty cool megaturn: that's $48, for six Provinces if there are somehow that many left by the time you're ready (but there won't be). The potential payload is even greater if you can use some Havens as a mini-Tactician, starting with ten cards instead of five. I don't think it's fast enough to beat a more straightforward strategy, but it is possible to set up a giant megaturn if you build long enough.
So I tried out my megaturn strategy, with mixed results. It turns out to be pretty hard to play, because of the very weak draw, and the weird timing of Haven (you want to play them only on the turn before your megaturn, but on the turn before
that it's very hard to avoid playing them, since they're stop cards otherwise). I'm also not sure what the ideal number of Ironworks is: 3 seems to work reasonably well, but I have trouble being patient enough to trash them to clean up for the megaturn once I'm done with them. Really, adding any payload to this deck slows it down a
lot.
The best I did was on my third try, getting a
$50 turn with 7 buys on turn 16. Is that enough to beat Squire/Steward/money? Maybe not, but it's more competitive than I expected. I just played one game of Squire/Steward/money, and probably played it poorly, but if those two players had been against each other, it would have come down to first-player advantage: Steward+BM had only 25 points before
turn 16 (a deficit the megaturn can overcome); picking up the fifth Province on turn 16 makes the megaturn fall short.
So, my conclusion is that the Coppersmith thing isn't really that great, but it's not a big nombo like HME seemed to be suggesting (at least if played as a megaturn, rather than for repeated single-Province turns).