You don’t pay WHT on ETFs not listed in the US… so not an issue for me.
Also, I don’t think many have ever been able to predict the end of a bull run in any market. Not investing in a market just because it has been on a long bull run seems unwise to me… but that’s because personally I want a diversified portfolio across sectors and countries around the world… and I manage the portfolio purely to achieve the right proportions I want… other than a relatively small amount I set aside for speculation.
Ultimately the US bull run has been driven by a combination of slow-but-steady economic growth, record corporate profits and record low interest rates. It will come to an end but it doesn’t HAVE to come to an end with a quick or massive decline… but if it does… it does… and nothing will save you then anyway.