Traditional export control applied to advanced hardware is because the US doesn't want its adversaries to have access to things that erode the US military advantage. But most hardware is only controlled at the high-end of the market. Once a technology is commodotized, the low-end stuff is usually widely proliferated. Night vision goggles are an example, only the latest generation technology is controlled, and low-end stuff can be bought online and shipped worldwide.

Applying this to your thoughts about AI, is that as the efficiency of training gets better, the ability to train models is commodotized, and those models would not be considered to be advantageous and would not need to be controlled. So maybe setting the export control based on the number of operations is a good idea- it naturally allows efficiently trained models to be exported since they wouldn't be hard to train in other countries anyway.

As computing power scales maybe the 10^26 limit will need to be revised, but setting the limit based on the scale of the training is a good idea since it is actually measurable. You couldn't realistically set the limit based on the capability of the model since benchmarks seem become irrelevant every few months due to contamination.