Dont they just out survive them, usually comes down to VP battles, volks can put up with a lot of abuse from late game units, arty, rifles cant, they start having less and less time on the field, volks more. Its not like rifles drastically out dps them, they can stand there and ignore rifles for quite some time. They can still anyway just throw flame nade, make rifles move volks win.
So how does vet 4 allow them to outsurvive riflemen in the situations you mentioned?