1. The human land on planet earth (no way you can argue this), and yet there is no mention of them in this supposed earth history.
I could write 2 pages on this line. Short answer... there is something like this in the earliest writings in cuneiform. Volumes have been written about the Anunnaki, so I will encourage you to investigate that on your own.
But in short, and according to currently accepted history, 500,000 years ago we took an amazing genetic leap:
Our brains quintupled in size, something no other species on the planet has done thru evolution.
Our hands went from grasping limbs and rudimentary rock tools, to shaping wood and rock into tools, creating art, farms, trading posts, ships...
We survived at least one great flood, maybe more, and the little Ice age that are rated as extinction level events for thousands of species, without help? Without some fore knowledge or forecasting ability?
Possible I suppose, but I see plenty of room for something LIKE humans landing and polluting our genetic pool... teaching, guiding, helping avoid planetary catastrophe, and yes eventually lost to history, or dismissed as gods or myth after thousands of retellings thru oral histories.
2. They destroyed most of the fleet but did retain at least one raptor shuttle and you are going to tell me that nothing of these people was dug up at any time.
Well, we can insert the "Yet" argument here... that they had not dug up a Viking longboat, until they did. Maybe they just haven't found Adama's Raptor YET!
But I can only imagine ANY tool or personal items of these "genetically compatible" and advanced race members was coveted, passed down, traded at high value and eventually worn out, lost, or destroyed to keep away from someone else. So it is conceivable to me, that all traces of an advanced race that could not duplicate it's items, would eventually be lost to history.
Consider, You take a firestick (magnesium and steel sparking tool), machete, axe, and some cast iron cook ware to a deserted island. After 20 years of constant use... the firestick and the cast iron (if treated well) might still be useful. Worn, but worth keeping. How much better of an axe do you think they had on Galactica? What exactly would you be looking at after 20-50 generations of use?
The Raptor... well, they never say what Adama did after he buried Roslin. That could be a whole series unto itself if he didn't fly it into the sun as a spectacular suicide.
Maybe they used it communally until it ran out of fuel and then recycled it down to the seat belts.
I agree with you the ending seemed rushed, I'm not sure if they WERE rushed, tired of it (writers AND actors), or trying to leave some loose ends to try and squeeze out a series of what happened to "Humanity".
I woulda watched it.