It seems to me that these design constraints are more to their benefit than to the benefit of the users because it simplifies a lot the maintenance of their infrastructure:
- By relying purely on phone numbers for user accounts, they remove a good chunk of infrastructure for having to deal with problems with logging in or missing passwords or stealing accounts.
- And by relying on Google Play Services, they avoid having to maintain a push notification infrastructure.
And I'm okay with this! It's smart and effective but I just wish he would be open and honest about it and not spread FUD about decentralization and other alternatives as an attempt to justify Signal's design decisions and make it look like "the only true way of messaging securely".
When he was asked by the public during his talk about the phone numbers, he went a long way to give an answer that didn't really answer the question. It was almost like a politician trying to justify an ulterior decision.
He is a salesman, a very good salesman. A good part of his presentation was not even about the "ecosystem", he just was wandering off-topic walking the public through his point of view. You could see this when he started to sneakily dismiss decentralization with saying "I host my own email" basically saying "So I am an authority on everything about decentralization".