Also - you don't start with 70 in any skill. Not even close. If you want to drag your ass around in slow moving armor for 20 levels because of the end game payoff, go for it. But there is a reason you might not want to start off in that stuff.

Light armor pairs with the thief stone and has better stamina and mana regen.

And is lighter than heavy armor for 70 freaking skill points. Which means the entire beginning of the game. And you may not want to invest that heavy in your armor.

I like this answer.

1. From the perk descriptions it sounds to me like light armor + dual wielded 1-handed weapons might be a really good all out melee combat build.
Simply from using 2 1-handed melee weapons at once you're already probably using twice the stamina that a normal 1-handed warrior uses. Add in the increased attack rate feats for dual wielders and it goes up further to 2.4x stamina cost after the first increase and probably either 2.6x or 2.8x stamina cost after the second. And if you're dual wielding then you can't be using one hand to gain the benefit of the respite perk either. So I suspect that wind-walker may be basically mandatory for such a build.

2. The number of perks required for a light armor build is significantly lower than for a heavy armor build with conditioning, due to more prerequisites you don't really need. The same is true on the smithing side of things due to the longer chain to reach dragon smithing. Consider this light armor perk set:

light armor: agile defender 1-5, custom fit, unhindered, wind walker, deft movement
smithing: steel smithing 1, elven smithing 1, advanced armors 1, glass smithing 1, dragon smithing 2
total cost: 15 perks

the heavy armor with conditioning equivalent:
juggernought 1-5, fists of steel, cushioned, conditioning, well fitted, tower of strength, matching set, reflect blows
smithing: steel smithing 1, dwarven smithing 1, orcish smithing 1, ebony smithing 1, daedric smithing 1, dragon smithing 2
total cost: 19 perks

Not a totally fair comparison, because the heavy armor side has matching set while the light armor side doesn't, so maybe it should be 16 to 19 instead of 15 to 19. But some people won't be wearing matching armor anyway, so matching set will be worthless to them, and it's mandatory for the heavy armor build (a prereq for reflect blows) but optional for the light armor build.

In sum the delta is 2-4 perks - 2 if you exclude smithing and wear a matching set, 3 if you either include smithing OR don't match perfectly, and 4 if include smithing AND don't match perfectly. Split the difference and call it a 3 perk delta.

Is the extra benefits of heavy armor really worth a 3 perks and the loss of wind-walker? I would say that it's right on the borderline, a reasonable trade either way depending upon how much your build need extra stamina regen and extra perks.

3. Personally, I don't really want my mobility impaired that much until I manage to get my armor skill up to 70. I'd end up playing half my play time at low mobility.

Number of perks is lower by a whooping 3 perks, and you will take perk in daedric smiting anyway since it's the best weapon type in game and you can't improve it without it, so it's difference of 2 perks.

Dragon-smithing can't be used to make weapons? I guess I've never heard of dragon-weapons but I assumed that the smithing capstone worked for either armor or weapons. Otherwise, yeah, the smithing angle there needs to be rethought.

Also it's 1 perk to craft AND improve weapon and armor so it's 16vs18 total perks in the end. Smithing is made that way so in the end light and heavy armor wearers spend same number of perks.

I'd really like to know what makes you think there aren't Dragon-based weapons despite the fact that the perk description for Dragon smithing says there are.