Are we to believe they were secretly brilliant forever but they simply kept it a secret until they had power?

Devil's advocate, but this was sort of true for the two Koreas, and even China to some extent.

https://files.catbox.moe/fm89r7.png

Yet despite this, all 3 ethnic groups are still seen as very smart today.

Personally speaking, I also don't believe that Jews are genetically dumb. But circumstances like the U.S pouring billions of dollars into Israel and bombing their rivals, is what gives them a massive leg up. Take away the aid, and they would probably look like Ukraine or Russia.