I also have another ~4 yr old male cat who shows no signs of any irritation. I know that one cat may be more allergic to fleas than another, but he would still have bite sites, even if they did not bother him.
The vet would not hear anything that suggested it could be anything other than fleas, and acted like I was being unreasonable for suggesting anything.
We did start using a carpet powder that may be irritating her skin. He didn’t even give any cream or anything for her wounds, which the one looks pretty rough. I don’t know what it’s safe to use for cats.