The problem here is you have multiple questions and if you searched for those questions they have been discussed here multiple times:
- Sustainability of the paleo diet
- Five bizillion questions about fruit
- Paleolithic grain consumption?
I can't find it, but there was a question about what paleolithic people did if they couldn't find big game, and there are many types of animal products that are not big game. There are turtles, rodents, shellfish, fish, bugs, lizards...all kinds of things. So even if there was no mammoth, they were still eating animal products.
The very title of this question shows me that you are posting here without really looking through this site. If you believe we are misinterpreting things, you should first figure out what we believe. You will find a variety of opinions, some that may surprise you. Some people eat lots of fruit, other people eat very little meat. The truth is that Paleolithic hominids ate a variety of things, so you can chose a paleo diet that works for you.
Beyondveg.com is quite excellent for discussion of hominid morphology and diet. Yes, Ardipithecus ramidus and many other ancestral hominids ate mostly plants, but the hominids we are interested in are the ones that have our uniquely large brain. The bulk of the evidence is that in order to evolve that brain, we had to adapt to a source of dense calories and that was either increased animal products or cooked starch. Australopithecines and other mostly plant-eating hominids were significantly different from us, their digestive systems were adapted for more plant-based bulk and their brains didn't need as many calories because they were smaller.