DFC,
I quite agree that the PIC is not always going to be 100% certain and that there are some situations where having either pilot able to call stop or to action the RTO may be an advantage. However the fact is that the advice from the two major jet transport manufactures, based on many incidents, is for the PIC to call stop or go and to carry out the stopping actions. It might not be perfect, nothing ever will be, but that is what they reckon gives the best chance of a successful outcome to a high speed RTO decision whether it's a stop or go.
There are a very small number of airlines that disagree with that policy and go their own way but the vast majority, in my opinion quite rightly, stick with what Boeing and Airbus recommend.