There is a difference in being strong/courageous and being straight up rude. Using words like the ones he used, even when he is frustrated, is not something a leader should do. One can be a strong leader while still using diplomatic/polite words.
Examples? Putin is 100% against the US. Does he ever use words like "your mom's a whore"? No. But he is what people would consider a strong man. Xi Jinping also never used such words yet he is also a very strong and respected leader. Lee Kuan Yew was also a great strong leader and he never used such curse words.
Being a "working cannon" doesn't excuse you from being disrespectful and rude. When you are supposed to be the face of your country, you are expected to be polite and respectful to other leaders, no matter how frustrated or mad you are.