The use of favors shouldn't be overused, for if used too much, no matter how deep the bond, it will thin out.
With Grand Ivan, there's no need to say it, because Grand Ivan owes Gao Yang a great favor, and it's a big one. Initially, Gao Yang and Grand Ivan were business partners, and they still are, so Gao Yang never owed anything to Grand Ivan. Later on, Gao Yang genuinely saved Grand Ivan's life and that of his nephew Ivan. These debts of gratitude that Grand Ivan owes haven't been repaid yet, and now, Gao Yang is the one sustaining Grand Ivan's Arms Empire through hardship. Therefore, even if Gao Yang decides to let go, he can confidently stand in front of Grand Ivan and expect a 'thank you.'
As for Gao Yang's relationship with Morgan, it's quite unique. There's a debt of life-saving gratitude and intertwined interests. Since Gao Yang saved Morgan on the plains of South Sudan, it's become unclear who owes whom.
