https://www.disnat.com/centre-apprentissage/articles-experts/patric-saint-onge/investissements-etrangers-dans-un-reer-ou-dans-un-celi
Sorry the article is in french but it answers the question pretty clearly for us, Canadian investors.
In short, if you are holding US stocks in your TFSA, you are right, there is no fiscal impact on capital gain, just 15% taxes on dividend and interests right at the source (US side). Thats it. In RRSP, there is no fscal impact whatsoever.
But i guess its off topic...