Still, according to the ranking and discussion in other threads, Bank and Forge seem rather average: most of the time they are inferior to gold, but sometimes they get to shine.
You never want Gold instead of Bank. Okay, maybe sometimes you do, but it is very rare for Bank to be worse than Gold. It's not a lot better than Gold usually, but it's slightly better.
And Forge shines pretty often. It's worse than Count which is worse than Chapel, but it's better than Mint, and sometimes Count and Chapel aren't in the kingdom (actually that's usually the case) and no other card trashes your deck as efficiently as these four do unless you get very lucky with Doctor.
Agreed, Bank is almost never worse than Gold, and is usually better.
It's worse in a junked deck or a trimmed engine where you get at most 2 treasures in play.
I suggest that you try building a trimmed engine where you would want a Gold and can get at most 2 treasures in play and see how many Provinces you can buy with that deck.
The only situations where Gold is significantly better than Bank are when you want to buy a $5 card and your cards are Silver, Gold/Bank and 3 unusable cards, and when Gold/Bank is your only card. In every other situation you're probably getting the card you want anyway. And those situations are extremely rare. Every time you could buy a Province with a Gold, you can also buy one with a Bank, and there are actually relevant times when you can buy a Province with a Bank, but not with a Gold even in big money decks (4 Coppers and Gold/Bank, two Coppers, one Silver and Gold/Bank mostly).