You're right, we should include -weight and -metric in that too.
but there are too many keywords too include AND you can use -metric without specifying -gateway during route del and vice versa.
So [gateway [-weight] [netmask]] won't help much.
I prefer to use word selected instead of preferred.
words like cost, metric, preference are similar but have their own technical meaning in routing stack.
I don't want to accidentally confuse users.