The difference between an experienced leader and a novice one
Well! Personally, I think Dr. Abiy requires to help himself and learn from P. Isayas. It is far better to address formally than informal. Any president is not merely a friend or a buddy. The president is an agent of his people. When you address to the president, you are addressing to his people. Convincing him is like winning the people of his country, therefore it is necessary to have a little more attention.