I know eight people currently riding older versions of the Big Block (with the cutouts on the dropout) who have zero issues - one of them being 6'4", 220 lbs.

Why don't you try contacting All-City directly and ask them what was up with their old frames breaking, how they improved the dropouts and whether or not it's a problem now? They're very nice people and I'm sure they will disclose the information you're looking for.