Risk management design just doesn’t allow this type of guesswork into such critical phases of flight.
We're not talking about "guesswork". We're talking about charts that should be in the documentation for the aircraft that give time to accelerate to some point short of V1 that will tell the pilots whether they are accelerating properly. This should be independent of and a cross check on any other calculations made. I can't believe that the major airframe manufacturers don't have this data from their pre-production flight testing. Low acceleration can be caused by more than gross weight errors. Weak engines or a dragging brake could also be at fault and not have anything to do with input error by the crew.
Although the preliminary report will probably clarify this, it seems clear to most of us here that they weren't accelerating fast enough and should have recognized it. Although management should give them the tools to recognize insufficient acceleration, and maybe did, it seems like the crew was asleep until the end of the runway loomed in the windscreen.