Abrasive pastes are used by many of us and they work beautifully.
Remember that when the old advice was written they probably did not have the ability to create and sort by size the abrasive grains that we have now.
I would speculate that the old abrasive grains were coarser than what we have available today and the fine grit stuff was either not available to the average guy or he did not know that it existed.

Regarding the bump in your strop. If the application of strop conditioner and then rubbing with a glass bottle does not solve the problem then sand down the bump with some fine sandpaper or a pumice stone. The pumice stone is preferred. The rub the strop with a glass bottle followed by rubbing with the palm/heel of your hand. The oils in your hand will help condition the leather.


Hope this helps,