While the skill tree might appear to be a circle, it's really two paths leading to Dragon Armor, essentially forcing the player to commit to either the left or right side. Both sides end with Dragonscale Armor, which is the best light armor available in the game. Damage reduction from armor maxes out at 567 armor rating displayed in the inventory. With all relevant perks and 100 Heavy Armor skill, this is achievable with Legendary Steel Plate, therefore making the left side a viable choice for a heavy armor character (Steel Plate is obtainable via the Advanced Armor perk).
Now that this is brought up. I found it odd for Steel Plate, some of the best HA in the game, to be on the LA side. It woule have been better to have the Advanved Armors of each to be included on there side. Maybe an addition to high end armor and not just another perk.
