It could be more simply solved by effective placement of chryssalids. Hiding them around tight corners, doorways, etc. This way you don't spot them out in the open, but at the same time don't guarantee death just for finding them.
And like you say, damage isn't a problem with balancing chryssalids, because they kill fleshy targets instantly.
I remember once I was playing the terror mission where you have all the destroyed tanks lined up, on CI. I had finally managed to get a competent team raised up, and was advancing slowly. My only contacts were two chrysallids, who had promptly retreated. I reached the entrance to the warehouse, and was about to enter when I revealed some floaters. I got my men in a fortified position and opened fire, but more floaters arrived. I was confident enough that I would be able to fight them off, and kill two of the six. My men were all in heavy cover, so I ended my turn confident that only one person would die at most. It was then the chrysallids appeared. They jumped down from the roof of the warehouse, and immediately infected my sniper and heavy. I'm sure you can guess the rest of what happened.
So yeah, if a chryallid can get close then they can do some major damage. So all you'd need for the elite version really is improved AI and some improved stealth. Make them no longer make noise, and make them invisible if they don't move. So they sit in ambush, and let your squad go by. Then, once they are busy shooting at the main force of mutons, they burst out, taking down your most vital soldiers.