Now, now. I do not believe in leprechauns
And I very much suspect that they do not believe in me either.
It may well be true that there are only, perhaps, 70 or fewer planets in our galaxy where advanced civilizations could have ORIGINATED. That’s not the same as saying there are only 70 or so planets where advanced civilizations MIGHT CURRENTLY EXIST. Colonization, even of planets that are too short-lived, or that have environments not conducive for complex life-forms to have evolved, may well be common throughout the galaxy.
I suggested that interstellar propulsion systems might exist that we don’t yet know about. To infer from this suggestion that, therefore, we KNOW that alien spacecraft must use them, is a logical fallacy of monumental proportions. They MIGHT exist. Other advanced civilizations MIGHT use them. We don’t KNOW, one way or the other.
I agree that the Phoenix lights were most probably flares.
We should, however, keep our minds open to possibilities that presently seem outlandish - unlike Lord Kelvin who proved, to his own satisfaction at least, that heavier-than-air flying machines were impossible.
Perhaps the aliens, if they exist, don’t give much weight to the economic imperatives that seem so important to us humans. From our economic perspective, interstellar travel may well be a losing proposition. Perhaps our hypothetical aliens have quite different motivations.