Normally I would agree with you, however, I’ve tried both systems with multiple form of data, even recapturing and attempting new exports with raw footage. I’ve also taken some of the same data that wouldn’t export on the Mac Pro, and am able to export it on our Macbook Pro (as the capture scratch is on a shared volume).
It’s only occurring with the H264 codec. I am able to export any other codec, so I have the option to export and use Compressor, which I don’t usually mind, only we sometimes rent out our systems and need everything to be in working order so the clients can use whichever workflow they like/