I agree that they're different and that the differences are important, but doesn't Light Armor also have a 25% bonus matching set perk?
It is all percent based however, which means the actual numeric increase will always be lower the smaller the starting number is. This means if both armours are increased by the same percent, heavy would get a bigger numeric increase than light because of its higher starting value, putting it even further ahead than it was without perks.
Alright, I admit I didn't do the math or thought of it alot, just semed to be like that by the look of the perks.
Still, I don't think light armor perks should focus on defense, same about the heavy armor who focuses on agility.
When im im heavy armor - I want to feel HEAVY. Its something called immersion. Same about light armor, I want to feel agile but easy to cut through.
Thing is, they are both ARMOUR. So it seems natural that they both focus on defence to some extent. I understand the want for a distinct feel between the two, and I want that as well, but nothing so far seems to say there will not be. The perks for HA regarding stamina seem to draw it closer to the base line (as if not wearing armour), while the perks for LA take it beyond the base line, actually improving the character.
And of course, you do not have to take the non encumbered perk if you do not want to

There is a defense cap, usually 85. Depending on the ease at which the cap can be achieved, your theory on heavy armor being always more defensive than light armor might not hold.
We have also not yet looked into enchanting, smithing and conjuration perks which hints at the ability to increase armor defense values outside of the HA and LA. Put all these together, I believe LA can easily hit the defense cap.
I was thinking about this. I made a thread in the normal forums pointing out that if all the HA perks give 125% greater AR (armour rating) and there is a cap at 85 then the base level of HA must be 38ish, otherwise the perks would be useless when you get the highest rated armour. I.e. if it is over 38 you would not need all the HA defence perks to get a max rating which makes them totally useless.
As such, I presumed there may be another method in play in SR. Someone else pointed out it might be that the 20% armour increase it a total of 20%, (i.e. 4 ranks for 5), though I'm not sure on that. Either way, if there is once more a glass roof for us to hit, I find it hard thinking that Smithing + maxing out an armour perk tree would not be needed in reaching it.
We don't know how damage and armour will work yet. There wasn't a cap in MW although the formula used meant armour never provided 100% protection.
As I said above, I think they will probably take another method regarding armour than what we saw in OB. Chances are it may be like MW, or even FO:NV with its damage threshold.

I've no idea.