Ok, here is actual flight test data for a jet taking off:
Horizontal axis is runway distance. The three vertical dash lines are rotate, liftoff and obstacle.
AX is longitudinal acceleration measured by an accelerometer on board the aircraft. It starts as 0.2 g and then drag picks up with airspeed.
Peak longitudinal acceleration takes place at liftoff in this case, but this is not always the case. It also depends on where you measure it in the aircraft when there is a pitch rate. Near the tail it will be higher (centrifugal effect around the aircraft cg).
While established in the climb at 14 degrees pitch, the longitudinal acceleration is EXACTLY THE SAME as it was on the runway.
Now if you do not believe this flight test data and want to argue about it as well, I don't know what else I can do.