Armour is no more than a protective layer. Regardless of what guild a character belongs to, if they have 90 strength and spend 100 hours fighting in plate mail, they should be equally used to wearing it.
Now a fighter should generally spend more time fighting and be a higher C level since the paladin has all those holy services to attend to.... ;\) , and thus be more comfortable with the armour on that grounds. On the other hand, all those prayers may well pay off and Celebron may grant a paladin aid which puts them on more than even ground when it comes down to a fight.

Fighting is NOT a craft. Rather, it is an area of training, but this area of training has been specifically broken off into its own category: Combat. We could also break off other area of training, such as "Metal-Working", etc, etc, etc, but for simplicity we have lumped all OTHER areas of mundane training into a category called "Specialized".