No guard has already been somewhat denounced by a bunch of people, and I completely agree with them.
I also don't like Weak Armor. The whole strategy is very risk based, but is a 1 stage speed boost honestly worth the defense drop?
Think about it. CAP 4 is already vulnerable to a bunch of hazards, and then it gets hit by a physical move. Let's use stone edge as an example. CAP 4 is weak to stone edge, and it is very unlikely it will survive said stone edge after SR damage. After that, you get a +1 speed stat, and even this may not be effective, depending on the stats we give CAP 4. All the opponent will do is crush you with a priority move, and CAP 4 has ultimately died, because it has an overall crappy ability that isn't really going to make CAP 4 a success in the metagame.
The one way I see this working if CAP 4 has endure and reversal. If it endures the hit, and then uses reversal (it is assumed to go first due to speed boost (more on that later)), CAP 4 could be something. But this makes CAP 4 centered on only one strategy, and maybe another one which branches off of it, which would be the pinch berry tactic.
Coming with Weak armor is also the complication of speed. What should the speed stat be, in order for it outspeed most of the meta once it gets a boost? It obviously must be slower than most of the meta at first, because if it is faster, the whole point of weak armor is defeated. The metagame is too varied for this.
A summary of everything above, weak armor isn't worth basing a whole strategy and a pokemon around. I keep my vote behind Illusion and Unburden (which shouldn't have been dismissed so quickly, imo).