I think that we could probably all go for eating less meat and a lot more fruits and vegetables. The flesh of other animals tastes so good though!
Whenever I've been in shape I haven't stuck to any diet or strict regiment. It's pretty easy to loose weight (in principle, not in practice) if you do some moderate exercise (like take a run a few times a week, take the stairs, etc) and avoid restaurants and processed foods. I think when you start cooking for yourself, you'll end up eating a lot more raw "real" food and will find it hard to cook the really unhealthy stuff you might feel totally fine about ordering. It just kind of works itself out.
Yeah, that doesn't work for me. If I'm not thinking about health, I'm happy loading up on the cheese and fried things to a probably unhealthy degree - especially when I'm making it myself.
There are clearly diets that allow for more than survival. Just be careful saying we evolved to do X. It's easy to get your causal arrows mixed up.
I think the more likely answer is that humans are capable of surviving on all sorts of foods, not "there is one hunter gatherer diet and it contained very little meat."