Searching for Sophia was only half a season, we saw her running around lost for the first episode (or was it 2), then the search for 4 or 5 episodes, and then the reveal in Episode 7
Regarding the "sitting Zombies", we honestly have no way of knowing how long they were sitting there. For all we know, when we see a new one, they could've been survivors who only just died this morning or yesterday of Starvation. Every survivor will be come a Zombie when they die, so, as long as there are survivors, there are new Zombies waiting to be born.
So, yea, maybe a bit much to still have packs of 100s a year into the outbreak, and certainly I can't argue with you about the Heat and decomposition, but, the sitters and the continued prescence of Zombies isn't so unbelievable. And let's not forget, they do partake in 4 legged animal flesh (Rick's horse and the cow Dale found, for example)