This is a loaded explanation. Yes, war does require quick response, which is hard to achieve in a decentralized state. The small nuance is that war or similar events are comprising a tiny fraction of what a government does (not by impact, but by total amount of things to do). And guess what, direct voting is just fine and fast enough for such thinks as any and all taxes, industry wide restrictions or permissions, economic focus, foreign policy, immigration, healthcare, education, social security and so on.

> This is why the US didn't (and doesn't) have direct voting on war declaration

No, it's because the US doesn't have direct voting on any national issue; there is no legal provision for it afaik. US citizens only elect representatives, and they make the decisions.

> a handful of recent presidents decided that even Congress is too slow for them

What are you referring to?

No President before Trump II has entered a war without consulting Congress (and the people) and obtaining their support. After Japan bombed Pearl Harbor - when the US was most in direct peril in the last two centuries - Roosevelt spoke to Congress and the American people, and Congress declared war.

Most wars, however, don't have a formal declaration of war by Congress.