Setting up a test in a custom game lobby, I discovered the balance change for Echo in the Experimental Play card has no effect whatsoever and Echo reverts to a full 200 HP every time. This includes dealing enough damage to be above 100 health, be below 100 health, and have the duplicate be eliminated entirely.
I have included the following Custom Game Workshop code that is supposed to demonstrate the balance change but doesn’t. Simply press Q to duplicate the Symmetra and don’t touch anything as she fires on you. You can switch the three bottom rules on and off to demonstrate different amounts of damage.