> People have been writing infix math notation libraries for CL for exactly this reason.
People have writing these notation libraries, but then not actually using them.
Infix libraries for CL mostly exist to end arguments; "we have infix; Lispers choose not to use it, and you will understand why soon enough".
That said, I very rarely write code like this. I tend to split operations over multiple lines, so that you don't spend so much time digging into and out of nesting levels. Prefix notation is not ideal for reading math. People have been writing infix math notation libraries for CL for exactly this reason.
It's not a showstopper, though. Also, I do find that sometimes having + and < to be of arbitrary arity is really convenient and makes for nicer code.