Size-wise you've got to give Burley the edge. It'd be interesting to see Armstrong try and apply his pressure style against someone naturally bigger and super cute defensively. I don't think he could do it.
Another major thing is that burley looks much stronger than Armstrong does IMO. Burley looks clearly stronger than Smith, who looks clearly stronger than Moore. I don't think it needs to be said that Moore is stronger than Armstrong. I think if Burley could answer Hank physically, then Armstrong is in for a very long night IMO.
But how strong (or seasoned, for that matter) would Burley have been if we use the version that was actually contending for a WW title shot circa '38-41?
I think strength is innate and matters more about you as a person rather than actual size. Especially when the muscle he put on to move up was just that, muscle to put on to build up, not build strength. I think he'd have been strong enough still, although I do get your point. That's why I put 'if'.
Of course it matters when comparing different people, someone weak for a person weighing 200lbs is obviously gonna be stronger than someone incredibly strong who weights 100. But I think if someone who we know is strong as fuck at 155, would still be strong at 147. Same as someone who's weak at 100lbs will still be weak if they added another 30lbs of weight. Especially when the weight Burley added was artificial and wasn't added by someone working out to become stronger. He added the weight literally just for the sake of adding that weight. I think he'll still be strong enough for Armstrong at 147.
Burley was only around 20 years old when he first broke into the WW rankings, meaning he almost certainly hadn't yet reached physical maturity at that time. Filling out into a (jr.) MW from a WW was more likely than not a natural process rather than an "artificial" one. Without footage of him in those formative years, it's impossible to say with any degree of certainty how strong he was (or wasn't) at that stage of his career as compared to a later one.
Fair enough, maybe I'm just talked shite. I was going off the quote in the Ezzard Charles book where Burley implies he can fluctuate his weight to whatever suits him. I've always thought he moved up due to not getting a title shot, I didn't realize how young he was.