I do think Trade Port is better than Treasury. It can't get hit by attacks, gives a buy, and allows picking up green cards early. We have played games that never saw a Winter, although those are not common. On the other hand, Treasury, much like Lab when compared to Hireling, actually does something the turns it's played in, and needs not fear terminal collision. Also unlike Trade Port, it doesn't just stop doing anything. Instead, it becomes a Peddler. I'm not sure i'd pick up Treasury on many boards that have Trade Port, honestly. Colony Games might work, or games with a lot of junking that easily go into Winter for other reasons. I almost listed VP token cards, as those avoid buying Victory cards, but i don't think any works good with Treasury. Goons actively harms it. Games where you gain your VP cards rather than buy them would also work, but man, when do you need Treasury, then?
I guess in general is better than Trade Port the later in the game you are. It's not like you couldn't buy one or two Trade Ports, and then, when Winter approaches, switch for Treasuries. But yes, we're aware of the similarities, and it has been a constant topic when discussing Trade Port.
Also, the theme is actually that your Port freezes over in Winter.