Why do you say it's not ideal?

Because that is not what a bolt is designed to do. The c-clip is there because the axle does "float" a bit. Some of that float is within the range set by the shims, some is there due to the compression of the seal in the back side of the spindle. A bolt will never be "tight" and could come loose.

That said, the most ideal thing is to replace the axle. That is not very fun. After that, whatever method you find acceptable and functional is great. It either works or not. For the effort/time/money involved in axle replacement, I am not adverse to entertaining the idea of doing the bolt/washer thing.

Michael