A GFCI will also clear a ground fault an EGC won't. For instance, suppose someone touched a hot wire and a small amount of current went through his/her body to ground. The small amount of current would not open the OCPD but the GFCI should sense it and clear the fault.
Also a GFCI will not clear a hot to neutral fault at all.
So really for best protection you need both where the risk warrants it.
Correct, under direct contact conditions only a GFCI will save you.