Actually, brass is perfect for the application. Those screws have absolutely no other job other than to keep the washer on the spindle nut. They do not need to be tightened very much to do that job. Brass is also sacrificial, it saves both the spindle nut and the washer from getting chewed up.

The problem is that people do crank down on them and/or use the wrong screwdriver and then there are problems. Replacements in stainless are fine, but there will be a bit of galvanic corrosion between the screw and the spindle nut. I would suggest some anti-seize or those too will have to be extracted at some point in the future.

Good Luck
Michael