Maybe it was the wrong reason. However much he bulked up he was never able to hurt Wladamir Klitschko or handel him in the clinches.
If he had worked on his speed more he could have given him some problems.
The minimum weight that a fighter can make without detriment to their performence. In Spink's case it is under 175 lb's making him naturaly smaller than say Sam McVea who fought at 211 lb's.
You're telling me Byrd put weight on to fight at heavyweight for the WRONG REASON? Janitor, every modern lightheavyweight/cruiserweight/middleweight that fights at heavyweight puts on weight to fight in that division - Moorer, Byrd, two fighters that have been very successful as heavyweight, then Roy Jones, Toney etc etc.
Name me one modern athlete, who with the advantages of weight training, hasn't bulked up to fight at heavyweight? There are none. You can't possibly argue it'd be beneficial for the likes of Moorer to stay at 175lbs, it'd be suicide for them.
Yeh, Byrd lost to the best heavyweight of his era (apart from Lewis), but he still accomplished a lot, he was ranked the No.1 heavyweight in the world by the Ring going into 2006. I'm not saying he was an all-time great, but he was good.
Also, "natural fighting weight" and "natural weight" are two different concepts in my opinion, each an area as grey as the other.
Natural fighting weight is dependant very much so on age - Ask De La Hoya if he'd still like to make 130, ask Edison Miranda how tough it was for him all of a sudden to make 160 - Other factors also play a role, e.g., diet and amount of training. I really believe the "natural weight" theory is a myth.