Actually I thought whilst S&P500 is made up of us listed companies, but the nature of their business is quite globally diversified. Hence, it’s not intrinsically a “US Index” right?
The S&P 500 stocks collectively have
some U.S. "skew." That skew is diminishing with time, and it's nowhere near the equivalent of holding U.S. dollars or close proxies to U.S. dollars. Even so, I don't think you should overweight or underweight a particular country's stock market(s). Mainly because it's possible some other place besides Wall Street could develop into a stronger stock market competitor (which has little or nothing to do with currencies). Let the global index figure that out for you. Don't try to second guess that possible future.
essentially, as long as the asset is denominated in USD, he is long US dollars too
It depends on what you mean by "denominated." If you mean "it's listed and quoted in U.S. dollars," no, that's arbitrary. Oil, wheat, gold, diamonds, Picasso paintings, shares of Sea Limited, and the Straits Times Index stock fund EWS (yes, really) all happen to be listed and quoted in U.S. dollars. So what? That doesn't make any of those things U.S. dollars.
Go look at the bid board in a video of an art auction at Sotheby's. The bid board will list several currencies as the bidders offer higher and higher prices on a painting or other work of art. The painting is never any of those currencies. It's a painting. You merely
exchange a currency to buy the painting. And then you aren't holding that currency any more.
He can only sell and receive USD proceeds and will face the FX rate whatever it will be at that time
Only for immediate exchange purposes, for 5 minutes (or whatever). That doesn't matter, except as part of the transaction cost perhaps. Whatever you're holding you're holding. And if you're not holding U.S. dollars (or something well correlated with U.S. dollars, such as U.S. dollar denominated corporate bonds), then you're not exposed to U.S. dollars. You're exposed to how well Sea Limited does or doesn't do if you're holding that company's shares, for example.
I tend to disagree. The markets are affected by the liquidity available. In the case of ETH and BTC, market makers provide liquidity almost entirely in USD....
Do you really have to quibble about this? You're holding 80% of your investible net worth in USDC. I agree you're heavily tied to the U.S. dollar's fate. You don't have to factor your 20% (ETH and BTC) into that assessment. (Though I'd disagree with you to some extent. Pull up a BTC versus USD Index chart to see what I mean.)
Hmm the problem is that i don't want to change my portfolio risk exposure, other then the USD exposure portion.
OK, so if I can translate that, something like a global stock index fund is too "boring" because it isn't volatile enough for you. That the circa 55% peak to trough decline in stocks (as measured in U.S. dollar terms for the S&P 500 during the Global Financial Crisis) just isn't exciting enough for you.
Sure, no problem! Just pick a basket of more volatile stocks if you like, a subset of the total investible market. There are several such choices available. Then you're not holding U.S. dollars or U.S. dollar proxies, but you are holding higher expected volatility assets.