It is not a matter of looking good for others. He has to prove his position or his position as Emperor will be threatened by other angels of nobility.
Even if that doesn't happen, if he fails to show that he can protect his vassal, he will stop being able to recruit vassals which will make his heritage and qualifications as an angel stagnant.
If his heritage stops growing, it will make it easy for a rank 8 noble to overtake him in terms of heritage. Once that happens, he will lose his qualifications to be an angel of nobility to that demigod noble and be demoted to rank 8.
So his position as Emperor and the power that comes with it is at stake. This is why despite how slow this attack was and how much spiritual energy it cost him to create, and how many lives and how much property would be lost if the meteor striked the city, the Emperor felt satisfied with himself and felt that every cost was worth it.
