When Roy Batty spoke slowly It's because he's regulating an internal tension.and no issues with the way Leto's talking... In some ways kinda Roy Batty...
Leto speaking slowly is just him telling you that every word from his mouth is golden.
Its a big difference.
Put another way - listening to Roy Batty measuring his words is a bit scary. If I hear someone talking like Leto it's not intimidating or scary - I'd just want to bash him in the chops for being arrogant.