Not always. But if the difference in size and power isnt huge, then the skill may decide. On the other hand, try to imagine Valuev and Paquiao fight. Do you have Pac winning this because of the skill?
Size DOES matter. This is why we have 18 weight classes in professional boxing. Maybe 18 weight classes are more than needed, but it still is an indicator of the reality. Dawson is very talented, but he is not even a CW. His fans are not doing him good when they lose contact with the reality and exaggerate. A 2' 7'' tough giant in Vitali beating Arreola doesn't make Arreola a bum. He is a decent HW with power and endurance. I am not fan of Arreola, trying to defend him, but I am writing these sentences for the sake of defending the simple facts. It is so "annoying" to read all these ridiculous assertions made by delusional fans. I will give you a clue; this match between Arrreola and Dawson will "never" happen, not becasue Arreola is ducking Dawson, but because Dawson and his managers are far more sensible than all those clueless fans.