Daystrom Institute

It seems like some retconning, with the writers deciding that empathic characters are more interesting for storytelling than fully telepathic characters. It can be hard to create drama when someone on screen automatically knows what everyone else knows.

The Betazoids also didn't have black irises, which has previously been a distinguishing feature - albeit a feature that most viewers don't seem to notice. Given the many, many franchise references included in the first two episodes it looks like the showrunners are aware of established details, and that both the lack of telepathy and eye color are deliberate choices.

Edit: I read a suggestion here that maybe they do have dark contacts, except for Tarima, the president's daughter. Maybe the actor didn't want to wear contacts all day every day?

My impression was the president being deaf didn't have anything to do with the plot, but was probably about showing that deaf people are people who have stories too. The Betazoids delegates signing and speaking to each other might be something Troi has said previously: that it's rude to communicate telepathically among non-telepaths. But Lwaxana does it anyway because she doesn't care. Or it might have been to avoid confusion: "they're empathic with other species, but telepathic with each other? What is going on?" I don't know what is the significance of taking off the translation device.