Obviously they are hard to the average person, otherwise it would be super easy to field a QB. Duh. However, for a QB who makes it to an NFL roster, these are rudimentary throws that they are EXPECTED to make. This is why they make so much money. They are all capable of making those throws or they would not be NFL QB's. So yeah, Dak needs to make those throws because in the NFL, those are pretty routine.
Also, FYI, the throw to Cooper in the end zone that was picked was behind Cooper and lobbed so it was super easy to be picked off by virtually any DB. If you re watch the throw you will see the projectory of the football is headed behind Cooper. So much so, that if they were playing a friendly game of catch by themselves, I doubt Cooper could contort his body to catch that ball. It would be close. It was not a good throw at all. A good throw would have resulted in an easy TD. Cooper was wide open in NFL terms and Dak just had to not lob the ball and throw it out in front of Cooper more and it is a simple, easy TD.
