Agreed. Very often the opposite of these quotations could also be a rationality quote. No such quote is ever going to cover the full spectrum, and they will always be from the speaker's experience and reflecting his personality.

In context, then, it is worth pointing out that Canning was a politician who achieved perhaps his greatest success in wartime, and who is otherwise best known for running a highly active and aggressive (and successful) foreign policy, largely independently of the rest of the government. He's also notorious for having a duel against another Cabinet minister, which hugely damaged his career, so "impulsiveness and hot-headedness" is a yes. As Muir wrote:

[Canning had] immense confidence in his own ability, [and] often inspired either great friendship or deep dislike and distrust...he was a passionate, active, committed man who poured his energy into whatever he undertook. This was his strength and also his weakness.

Emphasis mine.