OK, 2 things:
Way off on the light year travel to Alpha Centauri: it is something like 4.36 light years from Earth.
But, oddly enough, that is kind of a distinction without a difference, because now, the only way for ET life to exist is for them to (1) travel the speed of light (2) and travel through some time space portal.
Having said that, you could pretty much make the statement that we cannot have been visited by ET/UFO's unless they (1) traveled the speed of light, and (2) by traveling speed of light, were able to make use of some time space portal.
OK, here's the deal, it is outlandish conjecture, I mean it is just a fantasy to say that those two things exist, or can exist. No one has ever defended a thesis or disseration on those two topics, nor any credible peer reviewed article.
So, I comeback to the position that Fermi first posed: Where did they come from?? Also, if they had gone to such a great length to come to this planet, I don't thing they would have been overly worried about the politeness of barging in on earth; obviously a scientific intelligence would have made no qualms about setting down, collecting life samples, making contact, exchanging ideas.
TO me it is just an argument that conclusively dispels the idea until someone can prove (1) travel at the speed of light is possible, or (2) some time space portal allows such travel. Until then, there is no possibility that we could have been visited.
I understand your position..
It's an old one held by many FREEPERS.
I also understand from a number of puzzle pieces and sources . . . that
MOSTLY, if not totally,
it's irrelevant to the facts as ET's know them and have been operating within for a very long time.
Some sources even assert that we can now operate similarly and have traveled some incredible distances and back routinely.
I don't know about that one. We shall see.
But if I had to bet from my collection of puzzle pieces, I'd bet that all your postulations and conjectures are . . . about as relevant to a computerized set of plans for a new Boeing jetliner . . . as a crayon.