the UK's Air Accidents Investigation Branch states that the crew, pushed for time, skipped the normal procedure which required them to estimate the take-off weight, and use this to crosscheck actual data.
It's nothing to do with laptops or "knowing" what the Vspeeds should be, it is simply a crew not following robust procedures and reaping the consequences.
If you don't find the time to do it right, how will you ever find the time to do it again?