Maybe, just maybe, fainting is a crucial part of the story. He is not well, and fainting so much is actually a very worrying issue.
I don't think the fainting is overused because the plot literally says his body is giving up on him. Fainting is part of the plot, he is literally unwell.
The issue is that the fainting has left the MC with no character agency. You can have anything as a crucial part of the story, but the readers should still feel like the characters' decisions have an impact of the plot. I have read many stories where the MC is extremely ill, but there is more plot going on that him fainting. Remember, a single part or element of the plot shouldn't consume the entire plot.
At last they are fixing the misunderstanding. Now the author doesn't need to use fainting as their main narrative tool