It is faster to solve 135 rather than 69, no matter if you use a CPU, a GPU, or a toaster. I think you missed the entire point. So your claim ("the chances are better with 1 GPU/CPU to scan for p69 than p135") has nothing to do with reality, as it contradicts a basic mathematical comparison of two terms.
If you have very limited computing power, isn't it better to try your long shot on 69 than on 135 due to the non linear nature of the odds of collision ?
I can ask the same question: if you have very limited computing power, isn't it better to try your long shot on 135 (and a lot higher throughput) than on 69 due to not knowing if you're gonna find the key at attempt #1 or at an attempt #2**68?
If you compare them both at their respective points of 50% probability that tends towards success, 135 will finish sooner.
The difference is that your odds of success in 1yr of bruting 69 are better than in 1yr of bruteforcing 135 because the work done does not compound the same way. That’s what I meant