Maybe...at level 51...I'm still not understanding something. Why is a weapon, such as Miraak's sword, with base damage of 16 better than an ebony greatsword (the sword of Falkreath) with adamage rating of 89?

I've sold or strored a lot of the quest related weapons simply because the base damage seemed insignificant compared to what I was carrying at the time.

All armor rating above 567 is meaningless, as the damage resistance is capped at that. Well, at 667, technically, as each body piece of armor gives a 25 AR hidden bonus. Which means that every armor from Steel Plate and up easily hits the damage resistance cap at Legendary quality, if you have all the AR increasing perks. Even low tier armor, such as regular steel, isn't that far behind, getting a bit above 500 without shield at Legendary. This is without fortifying Heavy Armor with enchantments, or through other abilities, such as the Lord Stone(+50 AR, as well as 25% magic resistance) or one of the Black Book abilities from Dragonborn, which gives all combat skills +10% efficiency, meaning even completely regular steel armor in Legendary quality will be less than 20 AR below the armor cap.

So, I'd say, go for the armor you think look the best. Personally I love using the regular steel armor for Nords, though I rarely get it up to the armor cap. Smithing is too much of a grind, so I tend to stop at Epic(Blacksmith's Philter + 20% smithing enchantment when at 50 Smithing does do the trick).

I merged three topics from the OP all asking more or less the same thing so the sequence of posts may be a bit confuzzling.

Can light armour reach the cap without investing in perks?

no, not unless you abuse the resoration loop.

becuase that is NOT its base damage, that is its base damamge + the boost from your two-handed skill and two-handed perks + possibly any enchantments. Its base damage rating is 22, BUT it is also A LOT slower then miraaks sword and you cannot hold an shield while using it.

Yeah, same here, steel armor is probably my favourite heavy armor.