I agree. Fraud can take several forms. Some are easier to catch than others. If dead people in Shannon County voted in numbers greater than Johnson's statewide margin, I think it is very likely that a judge would order a new election. However, I doubt that happened.
One thing I've not seen is how many of the Shannon County votes were cast at the polls and how many were absentee. One of the things to check is the signature of voters at the polling places versus a verified signature taken by investigators.
If most of the votes came in absentee, one can still do a signature check. However, my guess on absentees is that Democrat operatives simply sat down with people, ensured that they voted "correctly," and then had them sign the envelope. That would be hard to prove unless someone talks. It's also possible, if ballot security was loose, for the envelopes to be opened and the votes switched after the fact. That would also be hard to prove.
That has limited real value though. I worked in absentee ballots here in Arkansas this year, another fraud hotspot, and while nearly 25% of the ballots were challenged, our group found few signature discrepancies. The biggest discrepancies were in birthdate and there was an unlikely preponderance of ballots from "centurions".
The fraud largely needs to be nipped in the bud at the registration and request for absentee ballot levels. I'm not exactly sure how to go about that. The laws in various states are widely varied and what may work for one may not work in another, and I don't know that that could be in any way be standardized without furthur expanding the federal government's role which I don't think is the answer either. One thing is for sure though. If we don't do something pretty quickly, people will continue to lose faith in the electoral process and we will end up with a bigger mess than we have now, never being confident that the leaders who are serving are the ones who were elected.