I don't think that Develop is as weak as you suggest. It gives you 4 Silvers upon trashing Feodum and throws in a $5 card to boot, and it turns Estates into Silvers.
My impression of Feodum is the opposite. It's so hard for it to be worth much if an opponent plays defense correctly. Terminal Silver-gainers like Workshop, Ironworks, Armory, etc. gain Silvers at a snail's pace and has to gain Feodum as well. You need to be gaining basically a Silver almost every turn in order for a Feodum to be equivalent to a Province VP-wise by the end of a game against a decently strong BM-Province strategy.
The best way to maximize the VP from Feodum is to trash some of them. But that leaves fewer left over for you to have at the end of the game, and a sharp opponent can just take a couple from the pile to exacerbate the problem.
The good thing about Feodum is that it's fairly easy to pick up Duchies and even a Province every now and then, and it tends to be worth very little to opponents who do not pursue Feodum as a strategy (since a lot of decks, especially engines, don't end the game with 6 Silvers, much less 3).
(Also you wouldn't have won that game if you didn't trash the Feodum on the last turn. You would have had 16 Silver and 5 Feodums, but also 1 less Duchy, so 44 points. If you had bought a Silver instead of an Estate on the last turn, you would have tied.)
