Paper still needs a system to verify ballots aren't forged, and that system should be robust and transparent too.

The system is a whole bunch of people from different parties being present when votes are collected and counted. And with paper ballots you need to do the fraud in many different polling stations.

It is possible to do small-scale fraud with paper ballots, you can never fully eliminate that option. But it is exceedingly hard to do larger scale fraud without it being extremely obvious to any observer.