I wouldn't say either are crutches specifically... but i'd agree that liberty launcher is probably the worst rocket launcher in existence
lib launcher = give up a rocket for slightly faster rockets, greatly hampering your damage output in exchange for making rockets easier to place. sounds pretty crutchy to me.
black box = give up a rocket for some minor self healing, greatly hampering your damage output in exchange for minor survivability. sounds crutchy to me, although it actually has a use for decent soldiers.
to me they're like training wheels, but only the lib launcher actually teachs you something that you can apply to the regular rocket launcher, which is aim.