We tend to read that a bit differently. We think he meant that if it all turned out to be simple tangible craft etc. etc. etc. then it would not be as complex and interesting as he'd so far observed, researched it to be.
Our reading of Dr Vallee's 3? books depicted Vallee's perspective as fairly consistent across all of his books. He meticulously and tediously to the point of almost boredom documented how the ET/UFO stuff rather shockingly closely paralleled poltergeist and other dark occult goings on in the night through the centuries.
It did not seem to us that his perspective was all that diverse, at the point of his writing those books.
His thinking is very diverse on the issue; he has not ruled out entirely the ‘ET’ hypothesis. He’s actually pretty noncommittal when it comes to trying to nail this down - and that is in line with his main theme of the necessity of studying all of this scientifically.
I think he meant that the phenomena, historically, often echoed the beliefs that were current during the times when they displayed; and as we have grown more technologically advanced they have taken on the tone of our current cultural references. He recognized an element of - for want of a better word - the ‘psychological’. (I think the ‘control system’ that he suggests could very well be a collectively self-imposed one which is inherent to the development of our consciousness.)
He’s been doing online interviews over the past few years; you might be interested in how his thought developed after his earlier books.