>>Land dwelling four legged ruminants have their max fat stores in fall. By
spring, >>those animals have used up a lot of their fat.

Yes, but that's not the only source of fat in animals: archaeologic evidence
shows that early humans (just like most carnivore animals still do today)
broke up bones and skulls to eat the brains and tallow - the fattest parts.

I've been to serengeti and masai mara in kenya, and it 's easy to see that
big carnivores (lions, leopards etc) just eat up the entrails, brains and
tallow from long bones and leave the lean meat for the scavengers to finish.
Early humans should have done the same. 

But enough with the savannahs already, we should also consider "the
waterside hypothesis" that states that early humans fed consistently on
seashells and the like, so probably we overestimate the importance of meat
in paleo diet.