Astartes Armor and Astartes strength

The Astartes have super human strength, but they also wear power armor. Does the armor simply increase their strength, or is an Astartes more like a pilot inside his armor? I think there are a few instances where the armor’s power source is damaged and the Astartes can barely move inside his heavy armor, indicating the latter.

If so, I wonder if a normal human could wear a set of Astartes Armor made for his size.