Language has an influence on how one thinks. But this shower thought smacks of too great a generalization to me.

East Asians good at planning

This is already just patently false by painting with a huge brush. I live in Japan and I know plenty of people who are bad at planning. That said, Japanese society tends to value planning a lot and, because of strict work schedules, little time off, etc., people often do plan things way in advance.

I don't think kanji have anything to do with this. Korea doesn't use kanji (hanja) anymore in any regular way, so that would invalidate the theory.

There has been some debate about them being better at math because kanji for numbers are more straightforward, but I think that's been disproven IIRC.

I'm pretty sure there's a tons of example showing badly planned stuff in ww2 by the japanese and chinese army

That's a bit racist. Also kanjis are not hard, the rule is: top to bottom, right to left, the end.

你也可以不加思考就噴出一堆話，其實。 (zh-hant)

As for kanji, it's just practice and muscle memory, same as English spelling. Also, saying "East Asian" is just too broad.