I can assure this is a bad assumption to make. I have a tool to measure the frame rates when swapping Rx's of the same brand of Tx which debunks your theory. I have even seen cases where the same model of Rx were ever so slightly different. While I agree that the Tx may have a "Max Frame Rate" that it can support, it's still going to be limited to the quality of the Rx which I have personally observed as the variable across the many brands I listed above.