I note what you say. If these are degraded carvings in limestone, then they will certainly weather and erode more quickly than granite. The fact that the hills are made of limestone though would not rule out people having carved faces in them as English medieval sculptors often used the medium of limestone for carving statues, which still adorn the exterior of many of our cathedrals and churches. In the wet English climate they have not fared well and there has been an ongoing restoration project at many cathedrals to replace or repair them.
Although rain is the enemy of limestone, we are talking here of a site which is based in a desert. Hence, the points you make are certainly well made but I think we need to take into account the much drier conditions found here. Although the ancient Egyptians (whoever they were) built the three pyramids at Giza from granite, they used limestone for the outer casing stones, some of which still survive in situ - most of the missing casing stones were in fact used by the Arab conquerors of Egypt for their own building purposes.
I agree it is a very blurred photograph we are looking at and Joseph Farrell makes that point in his book. Moreover, the faces are shown in profile rather than a head on shot, which would probably have clinched the matter one way or the other. I wonder if Google Earth could come to our assistance.
As to pareidolia, yes that is always possible but then NASA makes that argument about the Face on Mars (a very old and much degraded structure) and the C's have confirmed that the Face is genuine.
Could an ancient, now forgotten, group of rock sculptors have carved faces on a hillside on such a large scale? Maybe, since we have another such precedent that has been mentioned on this thread in south-east Alberta in Canada, which clearly depicts a man with an elongated skull, suggesting the Nephilim were most likely in North America too. This, of course is the 'Badlands Guardian', which is a rock carving made on a vast scale:
See:
The Badlands Guardian: Geological Feature that Stunned the World
Nobody seems to know when it was carved but this region was, of course, under a giant icesheet during the last ice age, which suggests it must have been carved after the end of the ice age (otherwise it would have been destroyed by glacial action one would think). We should also recall that the Native American Indians (the 'red man') were the Atlanteans (the C's often seem to distinguish the Celts/Aryans from the Atlanteans, although the former did come to occupy the north of Atlantis and presumably mixed with the latter at some stage). The C's have also confirmed that the Atlanteans colonised Mars (over 50,000 years ago judging by their recent answers). It is thus interesting to note that Mars anomaly hunters have for years been identifying large scale rock carvings on Mars in official NASA photographs. Could the techniques they used have survived and been employed here on Earth?