The problem I find with the X-COM system is that it's NOT Darwinian by any stretch of the imagination.
My experience with Superhuman shows that once you get a fair way through the game, your elite commander is just as likely to die as a noob rookie. It's all down to accuracy of the aliens and a fair bit of pot luck with how your Skyranger is loaded out.
Also, as soon as you get the aliens using psionics in X-COM, you'll find your own guys - even high-up members of your squad - turning on each other until you have enough research and the correct facilities to create your own psi-squad.
There is no natural selection. There is only death. I'm 16 months through the game and have been through around six commanders, my latest surviving by hiding on board the Avenger right at the back whilst everyone else checks out the scenery. He's ready to back them up at a moment's notice I'm sure... though he does tend to sit in the pilot's seat a lot and make sure the engine's still running for some reason...
Anyway... back to the demo...
A Reticulan was shooting some green blob at me. I was pleased to see that closing down the distance on this homing-shot meant that it couldn't turn a tight enough circle to hit. and blew the Reticulan to shreds with a couple of shotguns. Did make me wonder about the usefulness of the Reticulan weapon though - I could pause the game and dodge it nine times out of ten... I'm assuming they have some more deadly kit as well, but already I'm forming tactics
May your terror missions always be infested with Chrysalids.