My experience is that it's pretty simple to confirm that calculations done by an EFB W&B system 'match' those done using the approved paper system, at the various extremes of the envelope.
I'm afraid your experience doesn't quite cut the mustard in respect of what is required to be done.
And on the paper system a pencil thickness can 'weigh' kilograms and accumulate to an inch of difference anyway...
Unfortunately, many loading systems of a graphical nature are poorly designed and your comment is valid. However, design the system well and the problem fades into background calculation noise.