It's possible mail-in voting would be fine but there have also been some pretty high profile vote counting screw ups in recent memory (last Iowa Dem Primary, Broward County 2016 and who can forget Florida 2000!). Maybe if there were a couple of years lead time and all parties could review the process to be satisfied that would be a reasonable plan. On short notice, it seems like going with something tried and true is the way to go.
As a Canadian, I find it strange that a compromise can't be struck here. I know elections in the US happen on a fixed schedule but in Canada they can be delayed. If people are so concerned about Covid maybe delay things 6 months, congress is basically a stalemate and nothing much is happening anyway. Both sides agree to continue to fund the gov't as is, pause judicial appointments and other such stuff and vote May 2021 for a slightly shortened next term.
