i would think fundamentally ST is coming from the angle that if one is likely to stay and incur bulk of living expenses in SG, being overly heavy into IWDA would also mean that the person would have to go through additional leg of usd/sgd fx exposure when unwinding, as compared to balancing it with some STI (SGD), which would bring down the exposure to "non-home" currency (USD)
* above edited*
NO, that's not correct. IWDA is not U.S. dollars. U.S. dollars are only the very brief (hyper brief) intermediate currency between liquidating IWDA and raising Singapore dollar proceeds. When you're holding IWDA, you're holding global stocks, period. Not any currency.
When you use your Singapore issued Visa credit card to buy a scarf in Switzerland, the scarf is not Swiss francs. But that particular seller wants (or at least highly prefers) Swiss francs in exchange for that scarf. (Buy a scarf in Korea and it's different. Even the same scarf.) So you plonk down your Visa card (hopefully a good one), the merchant runs it through the terminal, and the Visa network assigns Swiss francs to the merchant's account (a credit) and assigns a Singapore dollar debit to your account. In between, the Visa network converts Singapore dollars to U.S. dollars, then U.S. dollars to Swiss francs. On the major credit card networks U.S. dollars are always at least one of the currencies in the "loop" -- that's how it works.
Same thing with your IWDA sale, fundamentally. You're not holding U.S. dollars, but U.S. dollars are very briefly used as a transition currency to get your Singapore dollars. You sell IWDA, get some U.S. dollars, then immediately convert them at spot rate to Singapore dollars.
The key difference between IWDA and a scarf in Switzerland is that IWDA is (are) global stocks, a globally traded asset. There is no difference between IWDA purchased/sold from Singapore and IWDA purchased/sold from Botswana. It's all the same, and there is no currency "zone" for that asset. It's globally, electronically traded. So it absolutely doesn't matter that U.S. dollars are in the "loop." You'll never hold U.S. dollars more than a moment in that transaction, unless you want to. The U.S. dollars here are just like the U.S. dollars the Visa network uses: meaningless math in the middle, simply used because basically everything is convertible to/from U.S. dollars.
The real businesses that you're investing in do real business in U.S. dollars to a large extent. But also in Japanese yen, Omani rials, Turkish lira, euro, South African rand, and, yes, even Singapore dollars. It's a global stock fund.
To repeat, and it's very, very simple: the listing currency has NOTHING to do with the real value of the asset. The only way there's any relationship between the listing currency and the asset is when the asset itself has something to do with the currency. A U.S. Treasury bond fund, for example, is definitely highly U.S. dollar correlated because it's investing in U.S. dollar denominated bonds. A gold fund? Are those U.S. dollars, yen, euro, or Singapore dollars? No, it's gold. Gold is not any currency no matter what currency the gold fund is listed in.
ES3 and G3B aren't currencies either, but it's reasonable to assume that the 30 Straits Times Index stocks have, and will have, greater
correlation(*) to the Singapore dollar specifically than any/every global stock fund. But that doesn't mean a global stock fund is a currency either. A global stock fund will be more correlated to "bigger" currencies (in relative shares) simply because it's global, but that's as far as it goes.
(*) Correlation isn't even remotely close to equivalence, as anyone who has been buying and holding ES3 or G3B over the past several years can tell you, as they look at the Singapore dollar quoted value of ES3/G3B fall well into the red while even their Singapore Savings Bonds are in the black. These too are shares in real businesses, and SGX market participants have really whacked stocks here lately, lately due to the COVID-19 pandemic. However, other things being equal, I like lower prices for stocks when I'm buying them. Maybe long suffering STI investors who have accumulated and are accumulating ES3 or G3B will finally see some appreciation going forward. Maybe, who knows.