Dexterity is generally regarded as the cleric dump stat (though I suppose Intelligence could be compromised at a push), so heavy armour is usually the order of the day. Very few clerics wear anything other than heavy armour, in stark contrast to the plethora of fighters in light armour. Medium armour is generally of limited use apart from at low levels (where heavy armour is unaffordable) or very high levels (when mithril full plate starts becoming a regular occurence). At the mid levels, medium armour I'd even argue is inferior to light armour: +1 AC (breastplate vs. chain shirt) is not worth the reduction in speed. Compared with heavy armour, the benefits of "regular" medium armour (i.e. not mithril heavy armour) - faster run speed and armour check penalties, are marginal for a cleric. On balance, however, the removal of medium and heavy armour probably worsens the character's AC by three to four points, depending on Dexterity (a cleric with greater than 15 Dex I take to be very rare, even if elven).
The question of balance, however, is what are you balancing it against ? Vis-a-vis the core cleric, you're change is probably reasonable; however, when contrasted with other core classes, the cleric is still balanced even without medium and heavy armour proficiencies. The issue of what you're comparing the modified version with is the crucial point in deciding if compensation is necessary at all.
The question of balance, however, is what are you balancing it against ? Vis-a-vis the core cleric, you're change is probably reasonable; however, when contrasted with other core classes, the cleric is still balanced even without medium and heavy armour proficiencies. The issue of what you're comparing the modified version with is the crucial point in deciding if compensation is necessary at all.
