I'm not saying an attack can't be done, or that it won't happen. Honestly, I'd be very surprised if it doesn't and I fully agree with you on the additional security measures.

What I am saying is that it's very unlikely we wouldn't find out what's going on before the results are set in stone at any scale larger than the tiniest local elections (which if you altered a bunch of local elections enough to exert influence, you run into the same issue of being easily detected). This would still be massively damaging to the election process, especially if the attack goes deep enough to require the election to be re-run, but not the end of our democracy.