It's pretty obvious that Strength and Poise need refinement! And like Tolvo said, Str weapons crush PvE. But I don't think tweaking the systems in their favor would unbalance the game, and I kinda like your suggestions.
One of the main problems of Str weapons is that they're so heavy, which means you need to sacrifice on armor, which ends up counter-intuitively with Dex builds being able to stack armor more easily than Str builds. So making Str reduce the impact of a weapon's weight on equip burden is a good solution. I'd propose another one, though: that equip burden not necessarily be tied with End.
I myself like to have only enough End to be able to equip my gear, but then that leaves me sacrificing stamina. And Str builds, on the other hand, need to stack End to be able to equip all their gear, going above the maximum needed to max stamina, and end up needing to sacrifice on Vit. Either way you have to make sacrifices, but in this case Dex builds only sacrifice stamina whereas Str builds sacrifice Vit for an over-abundance of End. Which brings me to your other suggestion: poise for Str weapons. I like that one too--no need to elaborate on it! And I definitely agree that light armor sets needs some poise too. But I think From clued into that too, since in the DLC they gave us the Lord's Blade set.
But my suggestion would be to tie Equip Burden to both Str and Dex, instead of End. Say: raise Dex by 1 level, get +1 to equip burden; raise Str by 1 level, get +1.5 to equip burden. End would be for Stamina and... probably something else, but I can't think of anything right now. Vit only raises health, anyways; why should End be any different?
I think Dex's side-effect should be something different from improving casting speed, though. What you suggested for Str is directly tied to making a Str build, and I think Dex should also have a similar advantage, rather than something more-or-less unrelated to Dex builds. Maybe it could be tied to dodging?
(As for poise-breaking, I'm not 100% convinced it works as we think it does anyways. I do think a few weapons within the same weapon groups have different poise-breaking values, and it is most likely already tied to weight. But if that's only my impression and it isn't actually true, then I agree with you that it should be.)