I can agree with you on this, @roamer_1
IMO, these "aliens" have been on earth much longer than Homo Sapiens. Subterranean for one reason or another.
Subterranean - That also is quite well represented in history... Portals, and stuff coming up out of the earth. I think the emphasis should be in those directions, and the spaceman thing is a distraction away from it.
There is somewhat to tie the two together - Subterranean and portals - The thought being that beings would have a hard time navigating as they seem to be able to without portals or some such...
Won't subscribe to 'much longer'... That can't be substantiated. But it is sufficient to know that 'they' are often of a greater intellect - Some so much greater as to dwarf us. I do believe that they often possess a greater knowledge of things past too.
Humans are most likely the 'virus' which periodically need culling.
THAT is where your assertion that it happens in a cycle makes sense to me.
It seems to me to be more a matter of exposure. Something happens to make them able to handle the atmosphere (or some other condition)from time to time, or particular to region... And there is an influx. Sometimes that is nipped in the bud, little more than an incident... sometimes it is very broad.
I had entertained the whole 'Planet X' scenario for that purpose A planet coming by every 2000-3000 years would handily explain that influx (Planet X/Niburu has some minor traction in history too), or at least major ones. But the 'up out of the earth' or 'through portals' seems to carry more weight. In most cases though, the rulers, the ruling class beings, invariably come from the sky, or show up from the ocean.
That's not perfect (The 'ant people' of Hopi legend are entirely subterranean), but painting with broad strokes, it seems to fit.
That does not discount UFOs and SFOs, or at least, that is not my aim. They exist. They are often of a greater technology than ours, though just barely - Historically, their technology seems tied to man's.
But they are there. I have seen them often in the night sky. One of the poor things of city life is the inability to see the night sky. Country folks see weird stuff in the sky a lot. So rural people will be less likely to discount it.