I think you would be valid in that, if we were trying to turn out craftman.. we are not.
Think of it this way...they used to build houses using nails and hammers...they don't anymore.. nails sure.. hammers, not so much. They don't start a new guy putting up framing with a hammer.. it takes too long.. they give him and train him with a nail gun.
Tables are not the science.. not the actual math... they are a simple representation of how to plan...so is a dive computer. But while one is a planner, the other is real time.... huge difference. The slide rule (perhaps abacus would be better) is a tool to calculate a value... a calculator does the same thing...so why don't we just keep using that slide rule? After all, the tactile feel and physical movement are essential to knowing the number is correct.
There is, however, something very dark about a dive computer, secretly doing strange calculations and telling you what to do....