Even if you find that the bores are smooth and unmarked, that doesn't guarantee that you don't have any broken rings.
It's rare to lose cam lobes on all cylinders at the same time. Exhaust valves don't all go at once and severe valve recession doesn't usually affect all equally either. I'd certainly carefully reset the valve clearances and do another test. If you put a straight edge along the top of the valve train, have you got any high ones? This will usually mean valve recession and they will be exhaust valves.