The 15% US WHT is L2 withholding, applies to all US-domiciled ETFs (for Swiss residents).
Regarding the cost comparison tables, I was referring to Splitting the world: creating tax-advantaged global stocks portfolio using funds in 3a account - #7 by Dr.PI.
Some countries have lower L1 withholding when held by US-domiciled ETFs. If you have a particularly high allocation to these countries, a US ETF may be better. However, the difference is very small on average for ex-US.
The tables unfortunately don’t contain All-World ex-US (yet).