I think the takeaway here should be 'Stef outplayed his opponent' rather than 'Stef's engine strategy is the superior one for this board'.
I want to look at turn 3. He buys a duchy. You say you can't really disagree with this, but I certainly can (not that it's so simple to see; but this is definitely a mistake). He should definitely be picking up something else here - probably a vault, maybe a second bureaucrat, maybe a treasury, maybe even a city. The thing is, you opened treasury/- here. That does not look like you want to go for slog v slog duchy madness. Treasury is not such a good card for such a game - you are buying green too often for it to be much more than a peddler, and with as low money density as you'd have, it's one of the worst kinds of decks for peddlers. Also, you don't buy the copper, which you would definitely want to do in that kind of a deck.
So, turn 3 is probably even a little early for a straight mirror kind of match (though it's close; I would guess bureaucrat is better there though), but against an engine, it's definitely early. Since you've signalled so hard for engine, he should look to try to play against that - this is why I say vault. If he picks up vault, what can you do? Head for your engine anyway? What are you piling out for the cities? If you try to run the cities yourself, he can go big money, and since bureaucrat and vault both provide good longevity, I have to think he's going to be too far gone before you can get meaningful activation. And if you go for duchies, he has a choice. One is to let you go, and try to race for enough provinces - your deck is really not set up for a slog that well, it's not like you're going to run to all those duchies and enough dukes all that quickly. Still, that's so good against money that he will probably be compelled to join in on the duchies, IF you go duchy soon enough, i.e. before you get very many cities. But in this case, he has built up more than you , and can at least split the duchies probably, and outlast you though the slog. This is the problem with vault though, the mirror, because it only guarantees a duchy/duke, which silver comes pretty close to anyway, and the drawback is big against a duchy/duke opponent. Still, it can get you up to provinces sometimes too, which is massive if the duchies are split. So that's why I like it. Treasury and city give sort of split options, which can help him hedge his bets a little better (though city is mostly defensive against your engine, being a lab later on in a mirror, which is not all that hot).
Later on in the game, he gets pretty bad shuffle luck - his bureaucrat misses until turn 5, I assume you pass him an estate to leave him with $2 on turn 8 (and he doesn't buy copper.....), and he can only get 5 duchies on turn 10, when you're able to finish them off (and already have 2 cities, a gold, and an expand... you have actually bought MORE 5+ costs than him at that point...). He compounds things by just plowing ahead though. First, after you go city/masq/masq on turns 3-5, it should be VERY clear you aren't contesting duchy/duke, and he should slow down to build more. Even if you don't end up contesting those duchies, he is going to need 11 of those guys or more, and he needs more economy to be able to support that as quick as possible. Not to mention that it powers your city. Yet he continues buying duchy every chance he gets. He also continues not getting copper.
Now, let's look at the head down, I'm going to buy duchies every chance I get strategy he took. If he only gets 5-3, as in the game, he's basically dead. Let's go ahead and assume that you will get rid of all your duchies and estates and he'll have, well maybe 2 estates left. You are going to get all of the provinces by game end, because he can't dare contest you to speed things up, and he has no real way to 3 pile unless you really overbuy cities without being close enough to the lead. How many dukes does he need to overcome all the provinces? Well, that's 48 points, 15 are covered by duchies... this leaves 33 for dukes, which means 7. And of course, you can possibly buy say 2 at some point, to expand into provinces... and well, he's basically toast. If he gets 6 duchies, which is probably most likely, then he needs only 5 more dukes to balance out the provinces, though maybe with the farmlands, that's a little sketchy anyway. But this, this might be close - depend a bit on shuffle luck. 7 Duchies is really where he wants to be - there 4 more dukes will be sufficient, and he can almost certainly get that in time, then lock it away with number 5 and/or 6 at some convenience. But he's going to need to get quite lucky for that to happen. Note that if you don't contest at all, he DEFINITELY shouldn't get duchy #8 here, as it empties the pile for your cities (I'm presuming you'd buy these if you aren't getting the duchies). He has to think about not getting #7.
Now, given that this head down strategy probably turns out not so hot for him, he has another alternative, which is to go in for 3-4 duchies and then stop and start building. If you are going to contest, you are going to have to go pretty far in for duchies to pile out, which will slow you down. In the meantime, he can start grabbing cities of his own. This can be good, as he's going to have better longevity for the stalled out decks, though I have to think you're probably at an advantage there, since you're masquerades have trashed you down (they are VERY key for you here, along with city and expand).
This means that he probably needs to change something a bit earlier - again I'd point to turn 3 as optimal time, though turn 5 or 6 should really not be too late, and there it is clearly mistaken to be getting duchies, though again you draw REALLY well to put on SUCH a convincing demonstration.
Long story short, he failed to adapt to his situation, whereas you did, and that, along with some shuffle luck to make it lopsidedly gross instead of clear advantage you, is the story of this one, I think.
Oh, and I don't get your comment about downgrading to curses. What do you mean by that?
