Cheap cranks, cast rods, 2-bolt mains (on most), small runners, lousy head flow, yet....they fly on the street.
I'd have to disagree the head flow, on my flow bench a #48 flowed more than a Bowtie racing head; 240+ cfm stock vs 230 on the Bowtie, and flow is what makes power. No surprise to me why Pontiacs are stout performers on the street.
The biggest issue was always the cast rods as the nodular crank and 2 bolt mains can handle a fair bit of power. I've taken the stock rods past 6000 rpm with the engine ready for more (clean and strong) but not very often for fear of ventilating the block.
The small block Chev was never the best engine but almost always the cheapest; that's what it was designed to be.
