I think the argument for the early Asian math advantage is just what you state. In English, an additional translation is needed between the spoken numbers and the digits on the page, written one per decimal columns. Humans have very limited working memories, so the more compact and direct the numeric representation, the easier it makes mental arithmetic.
Regarding East Asians in STEM professions: I have been in Silicon Valley for most of the past twenty years, and can tell you that it has always been dominated by people of East Asian decent.
Additionally, here is a report from the National Science Foundation about the threat to US dominance in science and engineering from East Asia.