At a casual glance, any E2EE system can be reduced to your ironclad legally guaranteed (ILG) system by having the platform keep a copy of the key(s), for instance. So it doesn't have to be a one-or-the-other choice.
How does giving the platform the keys guarantee legal consequences for them if they use the keys to read your messages?
How does giving the platform the keys guarantee legal consequences for them if they use the keys to read your messages?