I agree that in Danish small words like "er" and word endings are often very difficult to detect. In Duolingo you can use the button with the tortoise icon to get every word pronounced separately - unfortunately the real world doesn't have this feature! ;-) So the normal speed audio prepares us better for conversations with Danes.
Okay, but in English, esp. when the verb "to be" gets its full force, there is a tendency to use the nominative pronouns even in speech: "it's me" vs. "it is I". ("It is me" sounds like you're trying to be all proper and formal, but don't know how.) I.e. when answering the phone, "yes, this is s/he" when you're the one being asked for. Also, when a relative clause follows the pronoun, then the nominative is practically obligatory even in speech: "it is he who made the mistake" (granted, in speech, one is far more likely to hear "he's the one who made the mistake". But if you start off with "it is" then you're stuck with the nominative pronoun when a relative pronoun follows.